Ansem, Seeker of Darkness
Ansem, Seeker of Darkness, sometimes referred to as Xehanort's Heartless, is the main antagonist of Kingdom Hearts and the "Reverse/Rebirth" scenario in Kingdom Hearts Chain of Memories, as well as a supporting antagonist in Kingdom Hearts 3D: Dream Drop Distance and Kingdom Hearts III. He is a member of the real Organization XIII and the Heartless of Terra-Xehanort, and as such his appearance and personality are primarily derived from Master Xehanort, and he retains his original form's "shadow".
Ansem was created when Terra-Xehanort, masquerading as Ansem the Wise, reawakened his sleeping memories and split his heart from his body, creating a Heartless; this Heartless, also named Ansem, appears to have characteristics of both Emblem and Pureblood Heartless, and it is unclear exactly which category he falls under. However, because Terra-Xehanort did this of his own will, he retained his memories in his new existence, and gained the ability to control the other Heartless. With their power, Ansem attacked the Realm of Light, intending to have the Heartless consume the hearts of every world and lead him to Kingdom Hearts.
Before Kingdom Hearts Birth by Sleep
On a quest from his original persona, Ansem travels back in time to when Xehanort lived on the Destiny Islands. Ansem entrusted his younger self with the mission to gather ten vessels to house fragments of Master Xehanort's heart to create the real Organization XIII so that they could create the χ-blade and restart the legendary Keyblade War. To accomplish this, Ansem gave Xehanort the power to travel forward into the future. Once his mission was done, young Xehanort would lose his memory of the event, although the subconscious memory would lead Xehanort to become a Keyblade Master. Ansem himself remained on the Destiny Islands until the time the Destiny Islands were destroyed, ensuring a version of him existed across time to allow his younger self the ability to travel to any time period.
Between Kingdom Hearts Birth by Sleep and Kingdom Hearts
Terra-Xehanort, at the time using his king's name, "Ansem", willingly gave his heart to the darkness in the pursuit of knowledge, creating both his Heartless and his Nobody, Xemnas. His Heartless was able to retain its selfhood for uncertain reasons, though it was believed by the first Ansem that this was due to Terra-Xehanort's willing abandonment of his heart. As a result, he could command the lesser Heartless without consequence. As a result, Ansem came to learn of the existence of Nobodies, including his counterpart Xemnas; the two collaborated to fullfill Master Xehanort's goal of obtaining the X-blade. 
Disguising his actions as an insatiable thirst for knowledge, Ansem sent the Heartless to many worlds in search for the Princesses of Heart to serve as the pure lights to forge the X-blade; many worlds fell in the process. Regardless if Xemnas could create thirteen darknesses, Ansem could create the lesser Keyblade of heart from the seven pure lights to open the Door to Darkness, which leads to Kingdom Hearts.
Fearing that a Keyblade wielder could still be out there, Ansem decide to test to see if there was a link between the pure lights and the Keyblade. Finding a special girl named Kairi, Ansem tossed her to the Ocean Between, but in truth, it was the charm Aqua placed on Kairi, and not her nature as a pure light, that led to her being drawn to Sora and Riku on the Destiny Islands.
Ansem traveled into the past, giving his younger self the task of traveling through time to collect hearts connected to them to be used in a second version of the Organization, as backup plan in case the first cannot collect enough vessels.
Ansem, as the Robed Figure, appears at Destiny Islands" keyhole shortly before its fall into darkness, noting that it has been "connected" and insulting Sora's ignorance of what was to come—however, as he is operating as a portal between times, he is not talking simply about how the islands will be consumed by the Heartless, but instead referencing how it will become a Sleeping World; the Sora and Riku from a year hence will travel back to this moment to follow Destiny Islands into the darkness, and in turn he will follow them. He vanishes when Sora's back is turned. Later, as Destiny Islands fell apart, Ansem opened a portal to Hollow Bastion for Riku, and following that, when the future Sora and Riku enter the Sleeping Worlds, he is there to call upon Ursula's phantom to attack them. After her defeat, Ansem again notes that the world has been connected.
Seeing the same kind of lust for power that he had once seen in Terra coming from Riku, Ansem appears before him following his battle with Sora. Riku is confused over why the Keyblade left him, to which Ansem explains; only a strong heart can wield a Keyblade. He tells Riku that to become stronger, he must open his heart to the darkness and let his entire being become one with it. Riku complies, opening himself to the darkness. However, Ansem uses this to possess Riku, regaining a body.
In control of Riku's body, Ansem meets with Maleficent as the Final Keyhole forms. He informs her that unlocking the Keyhole will allow the Heartless to overrun Hollow Bastion, but she is unconcerned, as she believes that she can use the darkness to rule the other worlds. Sneering, he creates the Keyblade of heart from six of the Princesses of Heart's hearts. As the Keyhole is not finished yet, Ansem notes it is because Kairi's heart is missing and without its power, they are at a standstill. Maleficent leaves him to guard the princesses, while she deals with Sora, Donald, and Goofy. After she is defeated, Ansem follows her to a hidden chamber, asking if she needs help. Once Sora sees him and the Keyblade of heart, Ansem tells him it can unlock the hearts, and demonstrates by stabbing Maleficent with it, transforming her into her dragon form. When the dragon is felled, Ansem notes that the dark fairy was arrogant to believe she controlled the Heartless when it was the other way around, and takes his leave, waiting for Sora in the Grand Hall.
Sora arrives, finally reunited with Kairi, though she is comatose due to the loss of her heart. Ansem comments that she lacks a heart, and from his impersonal comments and unusual nature, Sora realizes that who he sees as Riku is not truly the friend he knew. Riku introduces himself as "Ansem, Seeker of Darkness". The Heartless goes on to explain that Kairi's heart is in Sora, and that his dark Keyblade is necessary to remove the imprisoned heart. Sora refuses to agree with the plan and they battle. Sora wins the duel, and Ansem retreats. However, his efforts are not in vain, as Sora stabs himself with the dark Keyblade, in order to free Kairi's heart as well as the six other Princesses. This ends up opening the final Keyhole and the way to Kingdom Hearts, as well as the loss of Sora's heart and his brief transformation into Sora's Heartless.
Ansem shortly returns, having shaped Riku's body to resemble his original self, Terra-Xehanort. Now that the final Keyhole is open from Sora's sacrifice, he plans to kill Kairi now that her purpose in his plans has been fulfilled. Donald and Goofy bravely make a stand against Ansem in order to protect Kairi, but both know that, without Sora, they may not be able to stop him. Before he can dispose of the three, Riku projects himself from Xehanort's stolen body and manages to establish enough control to stop the Heartless in his tracks, allowing Donald and Goofy to escape with Kairi. This leads to an internal struggle between the two that Riku ultimately loses; Riku's heart is sent to the Dark World while Ansem takes complete control. Ansem then allows himself to be enveloped by the darkness flowing out of the Keyhole, and travels to the End of the World and Kingdom Hearts.
Around this time, Young Xehanort collected Ansem's heart to serve as a member of the second Organization XIII. However, his time ran out as he could not coexist with Master Xehanort at the time, and Ansem was forced to return to the past with his memory erased. Retrieved again from this point,[?] Ansem fulfilled his role in the new Organization. Following his defeat, Ansem's heart returned to its proper place in time.
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As Sora, his humanity having been restored by Kairi's light, arrives at the remnants of Destiny Islands at End of the World, Ansem appears, bearing Riku's form. He explains Riku's fall to darkness, that he desperately sought to escape the island "prison" enough to open his heart to darkness. Afterward, Ansem explains his philosophy: that worlds and hearts begin and end in darkness. Thus, darkness is the heart's true essence. Sora denies this, in words and in battle, with Ansem. During the battle Ansem summons both his familiar, the guardian, and a Darkside Heartless to assist him. As the battle rages on, Ansem leads the trio to the endless abyss where the Door to Darkness resides. This time, Ansem merges himself to the World of Chaos, a monstrous Heartless ship, and captures Donald and Goofy, though Sora rescues them.
After several more rounds of combat, Ansem, weakened, opens the Door to Darkness, imploring Kingdom Hearts to fill him with the power of darkness so that he can gain enough power to destroy Sora, Donald, and Goofy and shroud the universe in darkness. However, Ansem is horrified to see light pour out of the door. The overwhelming light of Kingdom Hearts envelops and destroys Ansem, allowing Riku to take back his body.
Kingdom Hearts Chain of Memories
Because Riku served as the host for Ansem, a piece of the Heartless remains even after his destruction by the light of Kingdom Hearts. Riku remained unaware of this until DiZ impersonated Ansem and sent Riku on a trial through Castle Oblivion to overcome his regret and fear of the darkness within him. When Lexaeus fights Riku, the resulting battle causes Riku to lose consciousness and Ansem takes control of his body, slaying the Nobody. However, before Ansem can cement his control over Riku, King Mickey's light seals him away for a time; this angers the Heartless to no end.
Eventually, Riku overcomes his fear of the darkness, intending to use it as well as the light. He also additionally receives some guidance from the enigmatic DiZ, the true owner of the mysterious voice, who in turn leads Riku to Naminé. Naminé offers to seal away Riku's darkness and Ansem, but he instead chooses to vanquish the Heartless. DiZ then gives Riku a card that will give Ansem form, so that Riku can finish him off once and for all.
Ansem again attempts to turn Riku to the darkness completely, and tries to defeat the young boy so that he can take possession of his body once more. Though this succeeds in destroying Ansem's consciousness, his power still lingers in Riku's heart. Riku sets off with King Mickey to rid himself of the Seeker of Darkness forever.
Kingdom Hearts 358/2 Days
Having been unable to find a way to rid himself of Ansem's remaining essence, it began taking over him and transforming Riku into a copy of Ansem. Riku kept it bay by blindfolding himself, and relying on his other senses to keep Ansem from completely taking over him. After learning Sora's memory cannot be completed without his Nobody Roxas, who holds the memories of Kairi in him, Riku knows that he might have to use the darkness to capture the Nobody and bring him to DiZ.
Riku catches up to Roxas at The World That Never Was, but Roxas proves to be too powerful and Riku is left with only one way to overwhelm the Nobody: unleashing his inner darkness. This allows Riku to manifest Xehanort's powerful guardian, who seizes Roxas and knocks him unconscious, but also forces Riku to take on Ansem's appearance. Feeling that he has sacrificed his identity, Riku takes on Ansem's name.
Kingdom Hearts II
During the Battle of the 1000 Heartless at Hollow Bastion, King Mickey reveals the truth about "Ansem" to Sora, Donald, and Goofy—the Heartless wasn't the real king of Radiant Garden, but the Heartless of an impostor. While the trio are shocked and dismayed to learn this, Mickey pacifies them by telling them that Ansem was still a powerful enemy that needed to be stopped.
Following the destruction of the Kingdom Hearts Encoder Ansem the Wise was using, the resulting explosion of light restores Riku to his normal form, implying that "Ansem" has finally been destroyed and his hold on Riku broken once and for all.
Kingdom Hearts coded
Yen Sid later explains to Mickey that the destruction of both Ansem and Xemnas has revived Xehanort and will lead to the restoration of Master Xehanort. Ansem appears along with Xemnas as one of Mickey's mental images.
Kingdom Hearts 3D: Dream Drop Distance
Ansem returns to become part of Master Xehanort's new Organization XIII, thanks to Young Xehanort's doings while time travelling. Accompanied by Young Xehanort, Ansem appears before Riku in La Cité des Cloches, stunning the young Keybearer, and offers him to become part of the darkness again, but Riku protests, reminding Ansem that he now walks the road to dawn. Undaunted, Ansem merely takes his leave.
When Sora is captured in the World That Never Was, Riku rushes to his rescue and runs into Ansem again. Ansem reveals that Riku had been traveling within Sora's dreams like a Dream Eater, and asks Riku to join him now that the boy has accepted his darkness. As they fight, Riku counters by asking Ansem to become part of his light, but Ansem ignores him and is eventually forced to retreat.
Once Riku finds Sora in the throne room with Mickey's help, Ansem appears before them along with Master Xehanort, Young Xehanort, Xemnas, Xigbar, Saïx and the rest of the new Organization. Master Xehanort proceeds to reveal that Ansem's possession of Riku's body, along with overseeing Maleficent's gathering of the Princesses, was all part of his master plan with Riku meant to become the vessel to complete the Organization. Ansem restrains Riku from trying to save Sora from becoming Master Xehanort's final vessel, but Lea's unexpected intervention distracts Ansem long enough for Riku to break free. Ansem summons his Guardian and has it grab Riku and Mickey, but the Guardian is defeated by Donald and Goofy. As the heroes advance, the Organization's allotted time expires and its members, including Ansem, retreat to their rightful points in time.
Kingdom Hearts III
Ansem first appears alongside his Nobody counterpart, Xemnas, outside of the Old Mansion, waiting for Sora. Seeking to use Roxas as a possible 13th member of the Real Organization XIII, Ansem and Xemnas tell Sora to give his heart to darkness, to recreate Roxas. They don't humor Sora's plan to recreate Roxas in the virtual Twilight Town created by Ansem the Wise, saying it's just data. After breaking Sora with their words, both leave through a Corridor of Darkness, after summoning a swarm of Neoshadows and Dusks for Sora, Donald and Goofy. After this, they watch Sora leave Twilight Town from a rooftop, just as Xigbar arrives to berate them. Ansem defends needing to be direct with guiding Sora, due to the boy being slow with hints.
Later, Ansem goes to the Dark World to retrieve his old master, as he wishes to know of the whereabouts of Subject X, a mysterious amnesiac girl that who had become his favorite test subject before her disappearance. Assuming she was taken away by Ansem the Wise, this brings him into conflict with Aqua, who kept Ansem company. Despite her resistance, Aqua could do nothing without her Keyblade, and was cast into the ocean by the One Behind, which causes her transformation into Anti-Aqua.
Bringing Ansem the Wise back to his old HQ at the Old Mansion, Ansem begs his treacherous apprentice to cease, as he doesn't wish for more victims. Xehanort's Heartless is not convinced by Ansem's act, reminding him of all the children sacrificed in their research on the heart, as well as his treatment of Roxas and Naminé. Suddenly, Hayner, Pence and Olette, who had been watching all along, enter into action. While Hayner distracts Xehanort's Heartless, Olette helps Ansem escape. The group is able to evade pursuit by Ansem thanks to a small troop of Dusks sent by Vexen, whose true loyalties lie with Ansem the Wise.
Ansem shows up for the last time in the Keyblade Graveyard, accompanying Master Xehanort alongside Xemnas, Young Xehanort and Vanitas, while he welcomes the Guardians of Light. Much later, he drops into the labyrinth for the final battle. Ansem, now without his Black Coat, fights against Riku alongside Dark Riku and Xigbar. Once Sora joins the fight, it doesn't take too long for Ansem to leave.
Ansem appears for the last time alongside Xemnas and Young Xehanort, as the last line of defense before Sora can reach the elderly Master Xehanort. Defeated by Sora, Riku and Mickey in a battle alongside his aforementioned incarnations, Ansem voices his final thoughts on his relationship with Riku, stating that Riku's might is "vaster than darkness" and showing he is proud the boy he chose as his vessel has grown into such a powerful Keyblade Master. Riku even states he is going to miss his nemesis. After their parting words, Ansem fades away into darkness.
Before possessing Riku, Ansem was little more than a wandering heart and could only appear as a figure in a brown hooded robe. This robe has two dark brown straps crossing over his shoulders and chest with five metal studs lining either strap. Due to his lack of a body, he appears much shorter and crippled in this form and wears the robe's hood up that hides his face.
Ansem gains a body by possessing Riku, though at first his presence is only evident from the change to Riku's voice. In his physical form, like his Nobody counterpart Xemnas, Ansem's skin color varies by being depicted as tan in the game to quite dark in official artwork. He shares Terra-Xehanort's long white hair, as well as the three spikes on the top and sides of his head, but he lacks Terra-Xehanort's bangs.
He wears silver-white gloves on his hands, each with a grey band on the wrist, while the rest of the glove, which has three black buttons lining one side, bells outwards. There is a black pauldron on both of his shoulders, each attached to his coat by two straps. He also wears black pants and black, silver-lined, knee-high boots identical to the ones worn by Organization XIII members.
Ansem's black leather coat is red on the inside and lined with yellow, and also has a large grey section that covers the lower half and shoulders of the coat. Upon closer inspection, this grey section seems to be attached by several small pins or buttons around the hip and neck sections of the coat, as well as by a belt that wraps around the Heartless's back and attaches to the rim of the coat. This coat is high-collared and completely unzipped, showing the second, shorter jacket the Heartless wears underneath. Ansem's second jacket is white and high-collared much like the outer coat. It is mostly unbuttoned and exposes Ansem's chest before being closed up by three buttons and two belts near the Heartless's waist, only to flare outward again, leaving three buttons undone. On the Heartless's chest is the Heartless emblem, but it seems to be just decoration as it appears attached to the long coat.
When Ansem becomes part of the World of Chaos, he loses both of his jackets and his gloves, showing a well-toned physique, and his pants and boots are replaced by a pair of black skin-tight leggings with yellow lining. He also grows to a tremendous size and his eyes become completely orange and pupil-less in this form.
As Ansem is essentially the Heartless of Master Xehanort, his overall appearance is nearly identical to a younger version of Master Xehanort, wearing the elderly Xehanort's attire.
Ansem is, thus far, one of only three Heartless with human-level intelligence, the others being Sora's Heartless and Scar. His knowledge of the worlds and hearts shows that Xehanort's keen intellect has survived the transition into a Heartless. However, the few shreds of humanity which remained in the researcher have been obliterated. Ansem is cold, calculating, and utterly ruthless. He treats people and their hearts as either tools to be manipulated and disposed of, or as cattle for his ravenous Heartless legions. He reveres power and knowledge above all things, and he despises ignorance.
The only times when Ansem's voice rises above a cold, monotonous drone is when he is berating Sora for his foolishness, or when he is reveling in his latest triumph. However, Ansem's scientific genius is blinded by obsession with the darkness. His arrogance ultimately leads to his destruction when the door to Kingdom Hearts is opened, and his greatest thesis is, in the end, proved wrong.
Ansem prefers to not fight hand-to-hand. Rather, using his dark powers and the One Behind.
Kingdom Hearts Birth by Sleep reveals that Ansem is essentially the Heartless of Master Xehanort. This is why he appears to share most of his personality traits with the elderly Keyblade Master, demonstrated by his choice of words when facing Sora, Donald, and Goofy; this is also reflected in his desire to find, open, and become one with Kingdom Hearts itself.
By Kingdom Hearts III, Ansem shows pride in Riku's development since their first meeting; seeing Riku gain true strength as a Keyblade Master surpassing the power of darkness. At the very end, Ansem shows that he still values learning about the World, telling Riku to expand his horizons by going to seek more.
As a Heartless, Ansem has control over darkness, which he can use to attack others, steal hearts, and create Corridors of Darkness. He can also possess other beings, and has command over the Guardian.
Ansem can time travel without aid, as he is just a heart. However, he is limited to points in time where he existed; additionally, he can only briefly exist in those times he is not native to, unless a vessel is provided for his heart.
When Ansem takes possession over Riku's body to procure a physical form, his fighting capabilities increased greatly, and he gains the ability to fly. His new body allows him to fight alongside his guardian by having it possess others to trap them while he utilizes an energy shield to both protect himself and damage foes.
When necessary, Ansem becomes more powerful by merging with either his guardian or the World of Chaos.
Ansem does not wield a specific weapon.
While possessing Riku in Kingdom Hearts, he wields the Keyblade of heart, which was created from the six captured hearts of the Princesses of Heart. Later, in his World of Chaos form, Ansem wields a weapon as massive as he is, a dual-bladed Soul Eater halberd. When fought on his own, Ansem simply uses the power of darkness and his Guardian to attack opponents, aside from when he is fought in Kingdom Hearts III, where he only wields the power of darkness in battle due to having lost his Guardian. When he briefly possess Riku to take down Lexaeus, he wields his Soul Eater.
In Kingdom Hearts 3D: Dream Drop Distance, Ansem briefly wields Frollo's sword to threaten Riku, but does not actually use it to fight.
Notes and references