Kingdom Hearts (series)

Kingdom Hearts (キングダムハーツ) is a series of action role-playing games (RPG) developed and published by. It is a collaboration between Square Enix and under the direction of Tetsuya Nomura, a longtime Square character designer. Kingdom Hearts is a crossover between Square Enix and Disney based in a fictional universe. The heroes of the series clash against the multiple incarnations of the primary antagonist, Xehanort, throughout the series. The series centers around the main character, Sora's, search for his friends and his encounters with Disney and Square Enix characters in their worlds. Kingdom Hearts 3D: Dream Drop Distance included characters from ', another Square Enix property, while properties from and  ' were included in  Kingdom Hearts III.

The series consists of various games across different video game platforms which was initially a point of contention for many players who could not afford all the platforms, although in the 2010s, most of the games were released in compilations on the PlayStation 3 and later, the PlayStation 4. The main bulk of the series can all be played on PlayStation 4, and those that can not such as Kingdom Hearts 358/2 Days and Kingdom Hearts coded were adapted into movies for these compilations. Some of the games were re-released as remakes or enhanced ports with the subtitle "Final Mix". There are currently 14 main installments released in the series (bolded in the "Games" section below, although note that the tenth is a movie).

There have been several types of merchandise released along with the games, such as soundtracks, figurines, and companion books. In addition, the games have also been adapted into a manga series and novels.

Most of the games in the series have been both critically acclaimed and commercially successful, though each installment has seen varying levels of success. As of December 2006, the Kingdom Hearts series has shipped over ten million copies worldwide, with 2.0 million copies in PAL regions, 3.0 million copies in Japan, and 5.6 million copies in North America.

Overview

 * Further information: Characters of Kingdom Hearts

Kingdom Hearts features a mixture of familiar Disney and Square Enix characters, nearly all of them coming from the Final Fantasy series, as well as several new characters designed and created by Tetsuya Nomura. Though the series features locations unique to the Kingdom Hearts franchise, worlds from Disney films are heavily explored. Sora must visit these worlds and interact with popular Disney characters to protect them from enemies. Often, Sora's actions in these worlds follow closely to the stories featured in their accompanying Disney films. However, in later games in the series, there is less focus on the Final Fantasy aspects and more focus on the Kingdom Hearts characters, instead making small nods and references to Final Fantasy. In one of the dialogues, Donald Duck tells Sora not to interfere with the worlds too much, since such interference would cause problems. Moogles, small creatures from the Final Fantasy series, are another common element in the games. They provide the player with synthesis shops in order to create items for use in the game.

Creation and Influence
The Kingdom Hearts series is directed by Tetsuya Nomura, who also works as the character designer of the games. Nomura has stated that unlike working with Final Fantasy characters, keeping the main character Sora alive and interesting over multiple games is a challenge. He has also stated that though many of the Disney characters are not normally dark and serious, there were not many challenges making them so for the story, and despite this, their personalities shine because they maintain their own characteristics. Though Disney gave Nomura freedom in the characters and worlds used for the games, he and his staff tried to stay within the established roles of characters and boundaries of the worlds. When deciding which worlds to include in the game, the development staff tried to take into account worlds with Disney characters that would be interesting.

The inclusion of specific Final Fantasy characters was based on the opinions of fans and the development staff. Another criteria for inclusion was whether the staff felt the characters would fit into the storyline and in the Kingdom Hearts universe. Initially, Nomura was hesitant to use characters he did not design, because he was unfamiliar with the background work of such characters. For Kingdom Hearts II, he changed his mind after receiving pressure from his staff. Throughout the development of the games, Nomura has often left certain events and connections between characters unexplained until the release of future games. Nomura did this because he feels that games should have room for fans to speculate and use their imagination. He stated that with speculation, even though a game gets old, people can still be happy with it. In Kingdom Hearts 3D: Dream Drop Distance, Tetsuya Nomura used characters from The World Ends with You, another Square Enix series, and in Kingdom Hearts III a boss from Eihander was used.

Gameplay
The Kingdom Hearts series contains both 3rd-person fighting and role-playing game elements. The games are driven by a linear progression to the next story event, usually told in the form of a cutscene, though there are numerous side quests available that provide bonus benefits to the characters. Furthermore, there are allies to aid the main character, Sora. The allies in play rely fully on A.I. controls, though players could later modify and customize their ability usage frequency. The combat system takes on real-time, meaning Sora could engage the enemy directly; various actions, such as attack and magic, are executable, during or after the battle.

In Kingdom Hearts Chain of Memories and Kingdom Hearts Re:Chain of Memories the combat system was altered as Sora is no longer aided by his friends, and all of his combat commands are only executable via cards, with special attacks being executed with sleights. Additionally, combat no longer takes place in the same space as exploration; rather, whenever Sora engages an enemy, he is taken to a confined field for combat.

The Gummi Ship is another common theme in the series, where it serves as a means of transportation for Sora and company to travel towards other worlds. Players can modify and customize these ships via blueprints and selected parts. In the release of Kingdom Hearts Final Mix, the first game contained Gummi Ship side quests. However, due to the criticism regarding the complexity of the Gummi Ship customization, the third game's Gummi Ship was toned down, providing easier and wider modifications, allowing players to customize it into either a small classed battle ship, or a grand carrier.

Another recurring element of the Kingdom Hearts series is Jiminy's Journal, which functions as a bestiary and provides hints and simple character information. The journal also records Sora's minigame results, as well as unfinished side quests, allowing players to have easier resolutions to track the game.

In Kingdom Hearts II, the battle system introduced a new gameplay element: Drive Forms, which allow Sora to gain access to new abilities via his combat garment, and wielding two Keyblades for a limited time (however, not every form possess this ability). Magic is simpler to execute, and Sora's MP gauge will recharge automatically once it is used up. Another gameplay element introduced is the Reaction Command, various actions only executable in several specific situations. These actions vary from talking to a character to performing combat abilities in battle.

Kingdom Hearts Birth by Sleep introduced several new features to the series, such as Deck Commands, which allow you to use several unique attacks as well as items and magic, and the Dimension Link, which gives you access to several deck commands otherwise unavailable to the player. There is also the Shot Lock, which allows you to attack a multitude of enemies with many attacks, and the Focus Gauge, which is what allows you to use the Shot Lock feature. It also introduces Command Styles where the player gains the use of a different and more powerful combo. By filling up the command gauge with either attacks or deck commands, the player will be able to execute a powerful finish command. Which command you use is different depending on if the player is using a D-link or a command style.

The games are influenced by their parent franchise, Final Fantasy, and carry its gameplay elements over into their own action-based, hack-and-slash system. Like many traditional role-playing games, Kingdom Hearts features an experience point system which determines character development. As enemies are defeated, the player gains experience which culminate in a "level-up", where the characters grow stronger and gain access to new abilities. The amount of experience is shared with all party members and each character grows stronger as experience is gained.

Another recurring feature is the World music; all worlds have at least one normal field song and most have at least one battle theme.

Before The Age of Fairytales
Long ago before the great war was fought with Keyblades, it was fought by the physical manifestations of light and thirteen darknesses for great periods of times. Eventually, the Darkness removed their physical form becoming a single entity to defeat their counterpart, but its will could not be maintained and in order to expand and propagate their number, they slowly corrupted people’s hearts creating Pureblood Heartless. The Master of Masters and other Keyblade wielders begin to fight against the Heartless.

The Age of Fairytales
The Master trained six apprentices of his own, Ira, Aced, Invi, Gula, Ava and Luxu. Through the power of his Gazing Eye, the Master could see into the future. With this knowledge he created the Book of Prophecies save for Luxu and gave the others a copy of the book, upon reading it they were horrified of the last entry about the world's end in Darkness. Realizing that the passage was true; to prepare them the Master gave each apprentice their role; Ira as the leader, Aced supporting Ira, Invi as the mediator, Gula to discover the traitor, Ava create another group of devoid unions called the Dandelions. As for Luxu, to guard the Black Box, take the No Name keyblade to record and watch everything unfold between the others.

Before he disappeared the Master created the first Spirit Dream Eater Chirithy to help the Foretellers in their endeavors but warned them if a wielder's heart is corrupted by darkness or disappears, so will Chirithy. When the day came for the Foretellers to take their roles they created their unions each filled with countless wielders. One of those wielders,, met a boy with ever growing curiosity named Ephemer who wondered about their world and the two become friends. Overtime darkness crept its way into the world causing a rift between the Foretellers and soon their unions causing them to fight, meanwhile Player told Ephemer about the dream they had about them and decide to investigate the Clock Tower but after their first exploration he continues alone (unknown to Player he was invited to the join the Dandelions and become one of the new Union leaders).

Soon Ephemer's curiosity was right about the incoming Keyblade War and tried to warn Player through Skuld, they tried searching for him yielding no luck. Then, they come across Master Ava, informing them that Ephemer is with the Dandelions and invited them to join while Skuld accepted Player was indecisive worried about everyone else and asks their Chirithy for advice. When they decide not to join the war; Nightmare Chirithy gives Player a reason to fight and after defeating the Nightmare it claims that it was always apart of them as well as responsible for what's going on and after being defeated again despite combining with the Darklings the bond is now severed saying they'll meet in another dream. Dishearteningly Player ends up fighting in the war against all the Foretellers and countless wielders until they are the last survivor.

Then, as the ground is littered with Keyblades turning into the Keyblade Graveyard, Player is reunited with their Chirithy and bathed in light as they were shocked with tears of joy to see Skuld and Ephemer again as they leave for the new world.

Ventus's Surprising Past, the Missing Union Leader, and Darkness' Intentions
After the war the duty of preserving light is passed down to Ephemer, Skuld and their friends Brain, Lauriam and Ventus. They begin their new status as Union Leaders by combining unions and created the new spirit dream eaters called pets that would help the wielders forget the past (save for the Union Leaders). While reliving old along with new adventures the wielder's peace was broken when Darkness found them again but this time with ghostly apparitions appearing everywhere and the Darklings still pursuing them. Soon Lauriam noticed his younger sister Strelitzia was missing. With Brain's intellect the Union Leaders discovered that they swapped the real world for a data version of Daybreak Town and the glitches were a result of another world trying to connect, along with the Darklings, aware of the future ahead Brain promised to free them. In pursuing the creatures into the new world Ephemer and Player learned that the Darklings like Lauriam were looking for someone too.

Lauriam, continued to search for his sister with the help of Elrena and it led him to his comrades. Explaining the situation they knew that Strelitzia was apart of their group but was hesitant to join and that she had a great admiration for "someone" that she tried to save them from the war. Match Player's description, Ephemer takes Lauriam to meet them but was sad that they didn't know her either. As the mystery unravels Brain consults the book of prophecies and finds a note inside with a startling discovery he summons Ephemer to inform him that Strelitzia was the missing Union Leader. Knowing of her intentions but Player being here Brain figured out that there is an imposter in their ranks and with Ventus and Skuld arriving he asks them to remember their encounter with Master Ava. Hearing that Ven's encounter was different Brain reveals to him the shocking truth that he is the imposter. Knowing this wasn't Ava's plan and that he didn't know the Union Leaders suspected that Darkness may have done this and by pushing their comrade to remember Ventus recalls meeting Master Ava inside an abandoned building and left together heading towards the Clock Tower but not much else except for Strelitzia dying with that they resolve to help him and tell Lauriam what happened to his sister.

Meanwhile unknown to them, Maleficent came into their world led by the Darkness entity and despite Lauriam's efforts she escaped in one of the lifeboat pods unknowingly beginning the world's destruction. As the others returned to the tower the strain of remembering puts Ven to sleep while Brain, Ephemer and Skuld tried to figure out Darkness' next move aware that it was here but didn't know the entity's motive. Through his dreams Ventus remembered what really happened, it was Darkness that struck her down not him and Ven woke up distraught that he couldn't save her. Then, the other's conversation was misunderstood by a vengeful Lauriam who demanded to know what happened to Strelitzia but before his friends could explain Ventus reveals that he was responsible for her demise despite the other's protest. But the grief and anger knock him unconscious again revealing the true culprit to the group.

Meeting the entity the group discovered why it targeted Strelitzia as it played on Ven's hidden desire power but knowing of their comrade's gentle heart they knew he would never resort to such means. But Darkness believed gaining what was more important than how, realizing that his sister was gone for nothing Lauriam tried to avenge her but was easily defeated. The reason why Darkness hid inside Ventus was because it was written in the book by the Master discovering that it and the Master were friends. Discussing further the Union Leaders also find out that there were many willful darknesses around and the only reason they couldn't be seen was because they weren't acknowledged yet until now hearing enough Brain and the others decide to fight against the entity but with no physical form it couldn't be destroyed.

With Ephemer only standing despite being told that the entity had no goal Brain didn't believe that as it was still here. They found out that it was Darkness' intention to infect and expand by using Ventus' body they could separate from the whole and act independently. Lauriam finally accepts the truth about Strelitzia's fate and fights alongside the others with Player joining their ranks. Confidently the Union Leaders believed they could return to the real world only to be dashed when Darkness told them of the lifeboat's real purpose to be used as a last defense if Darkness couldn't be defeated and when used the world will be destroyed and sealed off with it already starting. Regardless they still fight briefly beating it back, the Darklings appear and come for Ventus but he awakens enveloped in light dispelling the creatures believing himself to be “pure light”. With that he decided to his power to give Darkness a form they could beat and fought the entity alone.

Hope for The Future and Xehanort's True Origins
With a brief reprieve, the Union Leaders wonder if everything Darkness said is true meanwhile the fight against the entity left Ventus unconscious again with Lauriam apologizing to him for his actions. Then, he was alerted with news that his sister is alive by Elrena as her Chirithy saw her walking with someone in a black coat. Shocked at first but remembering they are in data Daybreak Town and the Pride Shift the Union Leaders knew that all their data existed meaning someone could've accessed Strelitzia's. Hopeful that Strelitzia could be alive and worried about the state of the world. The group head to basement and found it was true as the world was being destroyed seeing the Ark room's condition and there were five pods left but with many trapped, little time and trying to keep hope alive the Union Leaders separate. Brain heads to the real world with Lauriam, Elrena and Ventus while Ephemer, Skuld and Player watch over the dandelions. Before leaving, he passed on his Master's Defender Keyblade and the Book of Prophecies to Ephemer.

In the real world, Brain tries to figure out how he can save everyone but couldn't so he resolves to save Ephemer and the others, and sent Lauriam, Elrena and Ventus into the future. Afterwards Brain is met upon Luxu who warns him that the Ark is incomplete and to use it properly the senders must have a medium and someone who remembers them at their destination and as for the data world being locked. Meanwhile the three friends are attacked by the remaining willful darknesses who wanted them to open the gate so they can spread but Ephemer, Skuld and Player refused however remembering their first encounter and realized they had little chance to survive. To save their friends and in a ploy to seal the darknesses away Player pretended to controlled by them and attacked Skuld and Ephemer before delivering the final blow Ephemer tearfully sent them through a gate along with the remaining darknesses. Inside the cable Player revealed deception and sealed the gate trapping them and reunites with their Chirithy one more time enveloped in light. Meanwhile as the two pods appear Ephemer and Skuld head for the real world to find them alone checking on the condition outside they see the world is being destroyed and like the others they attempt to leave for the future as the tower crumbles around them.

After the destruction, Daybreak Town is left underwater with Ephemer waking up from his pod, Lauriam wakes up in a field of flowers, Elrena is still unconscious on a stormy mountain, so is Ventus in the Badlands being found by an unknown person leaving Skuld unaccounted for. As for Player, inside the veil of light they see the sleeping Dandelions and their hearts being given to their Chirithys where Player's explains their other purpose when their wielder sleeps they assume another form to protect their hearts turning into the Dream Eaters that occupy the Sleeping Worlds. However the dream eater gives it's friend a choice to go to sleep or reincarnate as a new heart. Seeing a glimpse of the future Player decided to reincarnate saying goodnight to their Chirithy. Soon Luxu is seen walking through the Keyblade Graveyard with the Black Box and No Name Keyblade revealing Brain's face.

Meanwhile Brain wakes in an unknown town and meets Sigurd who explains that he is the only one to make it to this time and before leaving to his group's headquarters; Sigurd takes Brain to the fountain square to explain that he is in Scala ad Caelum and the mysterious person shows him a statue of the town's founder and first keyblade master. Arriving Brain was happy to see that it was his old friend Ephemer.

Overtime the Player's heart merges with that of a newborn named Xehanort.

Xehanort's Path as a Dark Seeker
For unknown reasons as a baby Xehanort was sent to Destiny Islands by a cloaked figure. Over the years growing up due to the heart merge he had dreams of Player's memories of the Keyblade War, seeing people and worlds he didn't know wanting answers and viewing his island to being so small he desired to see these worlds. Until one day, he was visited by Ansem, Seeker of Darkness, his Heartless from the future, who offered him a way off the island and Xehanort accepted. Getting his first taste of darkness his heart being affected by powerful negative emotions despite being horrified he was fascinated aware that his heart could still feel. He also believed that with a strong enough heart darkness could be channeled and controlled.

Returning to Scala ad Caelum he was taken in by Keyblade Master Odin, becoming his seventh apprentice. Through his training, Xehanort eventually came to see his fellow pupil Eraqus as a brother and as their favorite pastime the two often played a chess game called Alba & Ater. Then Xehanort and his fellow classmates were taught the ways of the Keyblade and their role as Keyblade wielders was to protect the worlds of light from darkness. However, he was unsatisfied with this ideal so he often visited other worlds without permission to learn more. To protect himself from the darkness between worlds during his travels, he was gifted Keyblade Armor.

Then, one day Xehanort and his classmates were informed by Master Odin that the upperclassmen of Keyblade wielders were missing, including Baldr's sister. In an effort to find them they split up into two groups to search the worlds with him, Eraqus and another apprentice, heading to Agrabah once there he realized that the world was still rebuilding from the destruction of the Keyblade War, as no humans were here. Then moved onto Wonderland, where they avoided the insanity of the Queen of Hearts, but Xehanort wondered if slaying those controlled by darkness was needed to protect the world.

Four years later, Xehanort was visiting the graves of his four fallen comrades believing their demise was his fault until Eraqus told him otherwise. Then, he planned to go out into the worlds to learn more before their Mark of Mastery exam and was told by his comrade to return before the exam. Returning to Wonderland, Xehanort found that time barely passed since his first visit. Still seeing the Queen of Hearts being influenced by darkness, her willingly approached her.

During his travels, Xehanort returned to Destiny Islands and reunited with his future Heartless, who gave him the power to time travel to gather 12 other incarnations of himself for the Real Organization XIII. After doing so as "Young Xehanort", he returned to his time, but forgot about his experiences from the future, while the memories were etched into his heart. With the exam drawing closer, Xehanort saw to travel again seeing darkness as something the worlds need, wanting to be on par with Eraqus and wishing of the world's equal balance. Traveling he met the Master of Masters, gained the black coat and believed that the worlds were under a "false light" wanting to change it overtime he possessed true strength over the darkness no longer needing his coat or armor.

Eventually, Eraqus and Xehanort became Keyblade Masters; while Eraqus became Odin's successor, Xehanort wandered the worlds. Gaining vast knowledge and in the midst of trying to unravel the mysteries of the Keyblades, the war and more Xehanort became obsessed. Diving deeper he came across something called the χ-blade and wanted to reenact the Keyblade War to forge it, to obtain the power of Kingdom Hearts so that he may create a balanced world. However, Xehanort grew very old, and devised a plan to use his Keyblade to extract his own heart and transfer it to a younger body to prolong his life until his ambitions were fulfilled. So he discussed his ideas about the Keyblade War with Eraqus, but when his comrade refused he continued on his own.

Then, he came across his pupil Ventus and trained him to use as a vessel in the Badlands but when Ventus refused to use the darkness inside of him the elderly master extracted it out of him creating Vanitas. With Ventus' condition Xehanort brought him to Destiny Islands so he could die in peace however Ven's heart comes across the heart of a new born Sora seeing that the merge allowed Ventus to live Xehanort continued to use him to forge the legendary blade and looked for a new vessel for his body and brought his comatose pupil to train under his old friend Master Eraqus.

Xehanort's Quest and The Origins of Sora
Three Keyblade apprentices, Terra, Aqua, and Ventus, train under Eraqus to become Keyblade Masters. However, one day, a Keyblade Master, Master Xehanort, mysteriously disappears, and at the same time, a vicious species known as the Unversed begin spreading throughout the worlds. Terra is sent to defeat the Unversed and locate Master Xehanort. Ventus is goaded into following Terra by Master Xehanort's enigmatic apprentice, Vanitas, and Aqua is instructed by Master Eraqus to bring Ventus back home and keep an eye on Terra. Along the way, Terra slowly begins to lose control in the darkness inside his heart, but finds solace with Master Xehanort, who appears to understand him.

Terra crosses paths with a young boy named Riku and chooses him as his successor. While in Radiant Garden, Aqua comes across her own successor Kairi and Ventus befriends fellow Keyblade apprentice, Mickey Mouse, and crosses paths with Vanitas several times learning what Xehanort did to him, what Vanitas and of Xehanort's plans to use him and Vanitas as part of his plan to forge the legendary χ-blade, capable of unlocking Kingdom Hearts itself. Ventus confronts Master Eraqus about this, who attempts to destroy him to stop the χ-blade's creation, but falls at the hands of Terra and Master Xehanort, the latter whom reveals his true intentions afterward.

Terra, Aqua and Ventus eventually battle both Master Xehanort and Vanitas in the Keyblade Graveyard, where they each meet their fates: Terra is possessed by Master Xehanort and transformed into the new Xehanort, but the new Xehanort is defeated by the Lingering Will, Terra's armor animated by his lost mind; Ventus is possessed by Vanitas, but he, Mickey and Aqua fight Vanitas together, Ventus mentally, and Aqua and Mickey physically, but though they manage to destroy Vanitas, the χ-blade and wipe the Unversed from existence, Ventus's heart is damaged and eventually makes contact with the heart of a young boy named Sora again, merging with it; Aqua places Ventus's now-comatose body to rest inside Castle Oblivion, and while looking for Terra, finds Xehanort in the Radiant Garden, where he was sent following the χ-blade's destruction, and battles him in an attempt to rescue Terra. During the ensuing fight, Terra temporarily regains control of his body, but Master Xehanort quickly retakes control and attempts to force Terra's heart out of the body, but darkness spills forth and Xehanort starts to vanish.

As Xehanort begins to sink into the Realm of Darkness, Aqua follows and sacrifices her armor and Keyblade to save Terra's body while she remains in the darkness. Xehanort, now with amnesia, is found by the sage king of Radiant Garden, Ansem the Wise, and taken in as his apprentice. Mickey passes his Mark of Mastery Exam under his master, Yen Sid, and is awarded the title of Keyblade Master. Inside Xehanort, Terra continues to counter him, vowing not to stop until he has foiled Master Xehanort and expelled him from his body.

The Great Danger That is to Come
During his apprenticeship with Ansem, Xehanort became one of his test subjects so he could recover his memory and so Ansem could learn more about the Darkness in an effort to defend his world but as the experiments continued Ansem worried about his amnesic apprentice's well being. Then, a lab was made below the castle for further study similar to Xehanort, Ansem had another subject an imprisoned amnesiac girl known as Subject X. Believing she disappeared due to the experiments snowballing out of control he ordered them to cease unknown to either that Braig secretly released her. Then he sank into despair over his error in experimenting on Xehanort.

Sometime later Xehanort opened the door in Ansem's basement, despite making Gummi Ship travel possible, Ansem worried about the world's stability. Soon he met King Mickey Mouse and they became great friends, conversing over many subjects, and finding solace in their companionship. Then, seeing Xehanort had continued the experiments in secret, accidentally creating the emblem Heartless Ansem forbade an further experimentation with the Heartless as they threatened the world's stability even more. Then, he accepted new apprentices Isa and Lea more devastating Ansem discovered the Ansem Reports, penned under his name, but written by Xehanort. He began to see that the damage he caused had become irreversible. To stop his interference, Ansem was sent to the Dark Realm by his apprentices allowing Radient Garden to fall into darkness continuing on Xehanort sent a young Kairi into the other worlds in attempt to find a keyblade wielder believing she was a Princess of Heart. Some time after, Xehanort began to reclaim his memories and his ability to use the Keyblade. Then, turning the blade on himself and apprentices he created their heartless and most of the Nobodies to form the original Organization XIII. With his body temporarily gone his desire to forge the x blade and claim Kingdom Hearts lived on his Heartless, Ansem, Seeker of Darkness, and his Nobody, Xemnas.

Sora's Journey Begins
Ten years later, the story focus shifts to Sora, Riku, and their friend, Kairi. The first game shows how Sora is separated from his friends when their world, Destiny Islands, is invaded by creatures known as the Heartless. During the invasion, Sora obtains the Keyblade, as Ventus's heart is still within him. Soon after finding himself in Traverse Town, Sora meets Donald Duck and Goofy, two emissaries from Disney Castle searching for the "key" per instructions from Mickey, their King. The three band together and travel to different Disney-themed worlds, sealing the Keyholes to the hearts of the worlds to prevent more Heartless invasions.

Along the way, they encounter a group of Disney villains, led by Maleficent, who is controlling the Heartless. Though they eventually defeat Maleficent, the three discover that Ansem, who has apparently succumbed to the darkness, is the true mastermind. Ansem's plan is to open the door to "Kingdom Hearts", a door which holds the hearts of all worlds, in the hopes of attaining eternal darkness. Sora, Donald, and Goofy defeat Ansem, and seal the door with the help of Riku and King Mickey on the other side of the door.

After sealing the door to Kingdom Hearts, Sora, Donald, and Goofy begin searching for Riku and King Mickey, finding themselves heading towards a mysterious fortress called Castle Oblivion. Upon entering the fortress, they begin to lose their memories. The three encounter a group of dark hooded villains (Marluxia, Larxene, Axel, and Vexen), part of a mysterious Organization. In the castle, Sora learns his memories have been manipulated by a girl named Naminé who was being held captive by the Organization. Sora, Donald and Goofy fight their way through Castle Oblivion and eventually encounter and destroy Marluxia, the lord of the castle, thus freeing Naminé from his grip.

To allow them to regain their memories, Naminé puts Sora, Donald, and Goofy to sleep for a year; in the process, they must lose the memories of their experience in Castle Oblivion. At the same time, Riku finds himself in the basement of the castle and begins traveling to the first floor with the aid of King Mickey. Riku fights both the Organization's members (Vexen, Lexaeus, and Zexion) and the darkness in his heart, particularly the remains of Ansem, learning to accept his dual nature between light and dark. Allying himself with the mysterious DiZ, Riku aids him in keeping Sora and Naminé until the former is awaken. However a snag in the plan over the year forces Riku to go after a young man named Roxas, the thirteenth member of the Organization to enable Sora's reawakening. Roxas, who had defected from the Organization earlier on after doubting their true motives and desiring to meet Sora in person, encounters Riku and defeats him easily at first, but Riku succumbs to the Darkness inside him and takes on the appearance of Ansem. With his newfound power, Riku subdues Roxas and takes him to DiZ, but the ordeal leaves him stuck in Ansem's form. With their plan successful, DiZ orders Riku to eliminate Naminé, but Riku refuses, and instead lets Naminé go with Axel, who turned on Marluxia and chose to aid Sora in Castle Oblivion and who was Roxas's best friend.

Xehanort Revealed
Seven days after Riku's success, Sora, Donald, and Goofy awaken in Twilight Town, with no memory of their time at Castle Oblivion, and resume their search for Riku and King Mickey. They learn of the Nobodies and are re-familiarized with their leaders, Organization XIII (Xemnas, Xigbar, Xaldin, Saïx, Luxord, and Demyx). Afterwards, Maleficent is resurrected and joins with Pete, another Disney villain, to find a new base of operations before resuming her quest for power and revenge on Sora. Sora once again travels to many Disney-themed worlds and resolves the troubles caused by not just Maleficent and Pete, but also Organization XIII whose members refer to him as Roxas. Meanwhile, Kairi is kidnapped by the Organization. They meet King Mickey, who reveals that the "Ansem" Sora defeated was actually the Heartless of Xehanort, who, sometime after being found by Ansem, betrayed his master and stole his name, and since then, Ansem the Wise has been missing. Furthermore, they learn that Xemnas, the leader of the Organization, is the Nobody of Xehanort.

The three arrive at the headquarters of Organization XIII, The World That Never Was, with their own artificial Kingdom Hearts looming overhead, crafted from all the Heartless Sora has defeated, with Sora defeating all the Organization members as he is finally reunited with Kairi and Riku, who reveals Roxas as Sora's Nobody (as well as Naminé as the Nobody of Kairi) that he captured by willingly assuming the form of Ansem so that Roxas could be defeated and absorbed back into Sora. While this occurs, Mickey finds DiZ, revealed to be a disguised Ansem the Wise, with a device to digitize some of Kingdom Hearts' power; as the others arrive, the system overload causes the machine to explode with Ansem consumed in the blast, apparently killing him, with Riku restored to his original state. At the top of the castle, Sora and his friends battle Xemnas, who uses the remnants of Kingdom Hearts to fight them. Refusing to accept defeat, Xemnas separates Sora and Riku from the others to fight them in a final battle that ends with his demise. Though trapped on the other side, Sora and Riku are able to return to their world, via the Door to Light, which was mysteriously triggered from Sora's heart.

The Key that Connects Everything
With the threat of the Heartless and Nobodies apparently over, Mickey, Donald and Goofy return to Disney Castle, where they stumble across a mysterious message written in Jiminy Cricket's Journal, "We must return to free them from their torment". Mickey digitizes the journal and creates a Sora made from Data to uncover the mystery. Following the journal's debugging, Mickey and Data-Sora find the source of the sentence: it was a message from Naminé, who integrated a data version of herself into the journal to inform Sora that he is the "Key that connects everything", and it is his duty to save those connected to his heart from their suffering, namely the real Naminé, Roxas, Xion (a replica of Roxas created by Xemnas as a fail safe in case Roxas or Sora proved useless to the Organization), and Axel, as well as Terra, Aqua and Ventus. Mickey sends Sora a bottled letter about this.

Back in the Realm of Darkness, Aqua stumbles across Ansem, who survived the explosion of the Kingdom Hearts Encoder, which sent him there. Ansem, with few of his memories remaining, fills Aqua in about his experiences with Sora, which brings Aqua to tears of joy, knowing Sora will come and rescue her and her friends. On Destiny Islands, Sora makes the decision to venture out to find and rescue his predecessors from their fates.

However, after successfully locating Aqua and Ventus's heart (thus leaving only Terra to be found), Mickey also receives the shocking news from Yen Sid that the destruction of Ansem and Xemnas has led to the return of Xehanort, and this will eventually bring back Master Xehanort. Seeing as Mickey alone is not enough to defeat what is not "a single one of [Xehanort]", Yen Sid orders Mickey to summon Sora and Riku to him to undertake a Mark of Mastery Exam to properly prepare them for their imminent clash with Master Xehanort.

The Return of Master Xehanort
Sora and Riku answer Yen Sid's call and he explains to them the details concerning Master Xehanort's rise and fall into darkness. Though Sora initially believes himself to be capable of beating Master Xehanort without becoming a Master, Riku readily agrees, in order to prove himself worthy of wielding the Keyblade, which makes Sora accept as well. Yen Sid assigns them to enter the Sleeping Worlds, where they are to locate and awaken seven worlds which were revived following Ansem's defeat but remained submerged in sleep, and in the process unlock the Keyhole of Sleep. If they are successful, they will be deemed Keyblade Masters.

But along the way, Sora and Riku become separated and each end up encountering a mysterious young man in a black coat with ties to Master Xehanort and accompanied by Ansem, Xemnas and Vanitas, whom they believed to have been defeated long ago. Ultimately, Sora's journey leads him to the World That Never Was instead of the Realm of Light, where he meets up with Xigbar and the young man himself, who reveals that he is actually Master Xehanort in his youth from the past, who was paid a visit via time travel by the disembodied Ansem, who sent him on a mission to travel to different periods of time to gather various incarnations of Xehanort to build the real Organization XIII. Sora fights his way to the castle, but is intercepted by Xemnas and ends up with his heart damaged, whereupon he falls into a coma and is taken to the castle by Young Xehanort.

Riku tracks Sora to the World That Never Was and finds him in the castle, where he battles and manages to defeat Young Xehanort with help from Mickey. Following the fight, Master Xehanort is finally revived, and reveals his true intentions: following his failure to use the χ-blade to summon Kingdom Hearts by pitting a heart of pure light against a heart of pure darkness, he has learned an alternate way of creating the χ-blade, since years before, after the Keyblade War, the χ-blade was shattered into thirteen darknesses and seven lights, and if Master Xehanort creates an Organization out of thirteen incarnations of himself, he will be able to recreate the χ-blade and start another Keyblade War. As Master Xehanort moves in to turn Sora into the thirteenth and final vessel for the Organization, Lea, Donald and Goofy arrive to aid Riku and Mickey, and Master Xehanort is forced to retreat with Young Xehanort, Ansem, Xemnas, Xigbar, Saïx and his other six hooded vessels.

Riku brings Sora's comatose body back to Yen Sid, where he dives into Sora's Dive to the Heart and collects the fragments of Sora's shattered heart, in the process battling a corrupted Sora himself and winning. Riku succeeds in waking Sora up, but Yen Sid only names Riku as a Keyblade Master for his efforts. Sora, undaunted by his failure, congratulates Riku and immediately after Lea shocks everybody present by summoning his own Keyblade, something he had only recently mastered and was unable to use against the Organization. After this, Sora departs again to train alone, not having been able to properly resist darkness.

With the knowledge of Master Xehanort's plans, Yen Sid orders Riku to bring Kairi to him so that she may undergo training with her Keyblade and become their seventh light to counter Master Xehanort's Organization XIII.

The Final Showdown
In order to thwart Master Xehanort's plans, Sora, Donald and Goofy embark on a quest to find Seven Guardians of Light and the "Key to Return Hearts", while Riku and Mickey search for previous Keyblade wielders.

E/E10+ Rating
Despite instances of mild censorship breaks, the Kingdom Hearts series keeps a majority of its content "child-friendly". It refrains from using profanity and making sexual references, as well as from dressing its female characters in revealing outfits. While these elements are common in the Final Fantasy series, Kingdom Hearts prides itself on maintaining Disney's values. Death and suicide are also not treated realistically in the series, often with characters disappearing, dying off-screen, being revived later, etc.

There are only five instances in the entire series where these rules are broken:
 * In Kingdom Hearts Chain of Memories, Axel uses the words "hell" and "damn".
 * The main reason Kingdom Hearts II received an E10+ rating, however, was the appearance of blood and alcohol in Port Royal.
 * Axel uses the word "damn" in conversation with Saïx in Kingdom Hearts 358/2 Days.
 * In Kingdom Hearts Birth by Sleep, Maleficent uses the word "Hell" (albeit referring to the plane of afterlife), before facing Aqua and Prince Phillip in battle.
 * "Hell" is used once again in Kingdom Hearts 3D: Dream Drop Distance by Sam Flynn, specifically when he argues with his father, Kevin Flynn, in one of the game's flashback sequences.

Games
For the most part, the series takes place in sequential order. The first game in the Kingdom Hearts timeline is Kingdom Hearts χ and intersects chronologically with the beginning of Kingdom Hearts χ Back Cover and the ending of Kingdom Hearts Union χ, followed by Kingdom Hearts Dark Road taking place many years later and Kingdom Hearts Birth by Sleep and Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-, which take place approximately 60 years after that again. The first Kingdom Hearts takes place 10 years after Kingdom Hearts Birth by Sleep and intersects chronologically with the ending of Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-. The direct sequels to Kingdom Hearts are Kingdom Hearts Chain of Memories and Kingdom Hearts 358/2 Days. The sequel to Kingdom Hearts 358/2 Days is Kingdom Hearts II, which takes place one year after Kingdom Hearts and intersects chronologically with the ending of Kingdom Hearts 358/2 Days. Kingdom Hearts coded, which takes place shortly after Xemnas's defeat and King Mickey's return to Disney Castle at the end of Kingdom Hearts II, leads into Kingdom Hearts 3D: Dream Drop Distance, which sets the stage for Kingdom Hearts III and the conclusion of the "Dark Seeker Saga".

The main games of the series and their remasters, remakes and companion releases, along with their original release dates follow:
 * 1)  (2002)
 * 2) *Kingdom Hearts Final Mix (2002)
 * 3) Kingdom Hearts Chain of Memories (2004)
 * 4) *Kingdom Hearts Re:Chain of Memories (2007)
 * 5) Kingdom Hearts II (2005)
 * 6) *Kingdom Hearts II Final Mix (2007)
 * 7) Kingdom Hearts coded (2008–2010)
 * 8) *Kingdom Hearts Re:coded (2010)
 * 9) Kingdom Hearts 358/2 Days (2009)
 * 10) Kingdom Hearts Birth by Sleep (2010)
 * 11) *Kingdom Hearts Birth by Sleep Final Mix (2011)
 * 12) Kingdom Hearts 3D: Dream Drop Distance (2012)
 * 13) *Kingdom Hearts Dream Drop Distance HD (2017)
 * 14) Kingdom Hearts χ (2013-2016)
 * 15) Kingdom Hearts Union χ (2015-2021)
 * 16) Kingdom Hearts χ Back Cover (2017)
 * 17) Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage- (2017)
 * 18) Kingdom Hearts III (2019)
 * 19) *Kingdom Hearts III Re Mind (2020)
 * 20) Kingdom Hearts Dark Road (2020-2021)
 * 21) Kingdom Hearts Melody of Memory (2020)

HD Collections
All titles of the series are collected in some form between five releases:
 * Kingdom Hearts HD 1.5 ReMIX (2013), including HD remasters of
 * Kingdom Hearts Final Mix
 * Kingdom Hearts Re:Chain of Memories
 * all Kingdom Hearts 358/2 Days cutscenes
 * Kingdom Hearts HD 2.5 ReMIX (2014), including HD remasters of
 * Kingdom Hearts II Final Mix
 * Kingdom Hearts Birth by Sleep Final Mix
 * all Kingdom Hearts Re:coded cutscenes
 * Kingdom Hearts HD 2.8 Final Chapter Prologue (2017), a compilation introducing
 * Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-, an original short game
 * Kingdom Hearts Dream Drop Distance HD, an HD remaster of Kingdom Hearts 3D
 * Kingdom Hearts χ Back Cover, an HD theater video that ties in the events from Kingdom Hearts χ
 * Kingdom Hearts HD 1.5 + 2.5 ReMIX (2017), including
 * Kingdom Hearts HD 1.5 ReMIX
 * Kingdom Hearts HD 2.5 ReMIX
 * a theater mode for Kingdom Hearts Final Mix (DLC)
 * an additional scene for Kingdom Hearts 358/2 Days (DLC)
 * Kingdom Hearts The Story So Far (2018)
 * Kingdom Hearts HD 1.5 + 2.5 ReMIX
 * Kingdom Hearts HD 2.8 Final Chapter Prologue
 * Kingdom Hearts All-In-One Package (2019)
 * Kingdom Hearts The Story So Far
 * Kingdom Hearts HD 1.5 + 2.5 ReMIX
 * Kingdom Hearts HD 2.8 Final Chapter Prologue
 * Kingdom Hearts III

Spin-offs

 * Kingdom Hearts V CAST
 * Kingdom Hearts Mobile

Two flash games were created to promote canon, important entries to the series:
 * Kingdom Hearts Re:coded Gummiship Studio
 * Kingdom Hearts Magical Puzzle Clash

Phases
The chronology of the Kingdom Hearts series is separated into three phases, according to its director, Tetsuya Nomura.
 * The Dark Seeker Saga, or the 1st Phase, portrays the conflict against Master Xehanort and his various incarnations. It spans all titles between the first Kingdom Hearts game to Kingdom Hearts III.
 * The χ series is set in the ancient past, long before the adventures of Sora. It consists of Kingdom Hearts χ and its related titles.
 * The 2nd Phase began with Kingdom Hearts Re Mind and will contain future titles of the series.

Trivia

 * Thirteen is a recurring number throughout the series:
 * It is primarily associated with Organization XIII and, by extension, Mushroom XIII, Finest Fantasy 13, and the thirteen floors of Castle Oblivion.
 * The Director's Secret Report XIII is a thirteen-part exposé by Tetsuya Nomura.
 * Riku's Session Limit includes an ability named "XIII Blades."
 * There are thirteen letters in "Kingdom Hearts."
 * Ars Arcanum consists of thirteen strikes if one includes the ability's follow-up attacks.
 * In Kingdom Hearts Birth by Sleep, one can fight a grand total of thirteen matches at the Mirage Arena (this is no longer the case in Kingdom Hearts Birth by Sleep Final Mix).
 * Thirteen Orichalcum+ are required to synthesize the Ultima Weapon in Kingdom Hearts II.
 * The sum of all the letters in the names "Sora, Riku, Kairi" is thirteen. The same is true for "Roxas, Sora, Xion," as well as for "Roxas, Axel, Xion."
 * There are thirteen letters in "Terra-Xehanort" and "Ventus-Vanitas."
 * There are thirteen letters in "End of the World," "Hollow Bastion," and "Radiant Garden."
 * Put together, there are thirteen letters in "Light" and "Darkness."
 * In Kingdom Hearts II, it takes thirteen hits to defeat Seifer for the first time.
 * Donald's Centurion has a strength increase of thirteen in Kingdom Hearts II Final Mix.
 * In Kingdom Hearts Re:coded, there are thirteen System Sectors, one of which contains thirteen floors.
 * Sora is "Combatant thirteen" when he faces Rinzler in The Grid. Sora was also intended to be the thirteenth member of the true Organization XIII.
 * In Kingdom Hearts 3D: Dream Drop Distance, there are thirteen Training Toy candies.
 * In Kingdom Hearts Chain of Memories, to enter the last room in Castle Oblivion, one needs a card value of thirteen or more.
 * Following the Keyblade War, the χ-blade was shattered into twenty pieces: thirteen of darkness, and seven of light.
 * The sum of the time displayed on the clock present No Name (and by extension, Young Xehanort's Keyblade), 8:05, is equal to thirteen.
 * Using the Restore Count reaction command during the battle against Marluxia's Absent Silhouette and Data Replica in Kingdom Hearts II Final Mix will restore the hit counter by thirteen points.
 * In Kingdom Hearts, the Keyhole in Neverland is located at the thirteen minute point on Big Ben's clock face.
 * There are 13 tracks original to Kingdom Hearts 358/2 Days.
 * The box art for Kingdom Hearts III features thirteen characters.
 * On a similar note, seven is also a recurring number:
 * It is mostly associated with the Seven Guardians of Light and the Princesses of Heart.
 * Sora's Fenrir has the highest strength increase of all his Kingdom Hearts II Keyblades, at +7. Similarly, Winner's Proof has the highest magic increase, also at seven.
 * There are seven magic spells Sora learns in the first game: Fire, Blizzard, Thunder, Cure, Aero, Gravity, and Stop.
 * Vanitas is fought up to seven times throughout Birth by Sleep: once by Terra, three times by Ventus, and three times by Aqua, not counting the Vanitas Remnant.
 * Roxas landed seven hits on DiZ's computer.
 * Roxas spends seven days in the simulated Twilight Town.
 * There are seven Orichalcum+ in both Kingdom Hearts II and Kingdom Hearts III.
 * There are seven tracks original to Kingdom Hearts Re:coded.
 * There are seven lights on the chandelier in the Garden of Assemblage in Kingdom Hearts III.
 * As stated before, the χ-blade was shattered into seven pieces of light.