Xion

Xion is the supposed fourteenth member of Organization XIII and first appears in the game Kingdom Hearts 358/2 Days, in which she could be viewed as both a main protagonist and antagonist. She is not actually a Nobody, and not even a true member of the Organization. Instead, she's an imperfect Replica of Sora as a fail-safe in case both Sora and Roxas proved to be useless to Organization XIII's plans. While this enables her to use the Keyblade, Xion's existence also halts Sora's progression of regaining his memories to fully awaken while in his pod, something which Naminé, DiZ, and Riku recognize.

As Sora's memories are the basis of her being, Xion initially resembles Kairi, who was Sora's strongest memory at the time of her birth, though her physical appearance eventually changes depending on who is viewing her and who they have connections with. Roxas, Axel, and Riku see her as Xion (and later as Sora), while Xemnas and Xigbar see her as Ventus, and Saïx sees her only as a hooded doll.

Xion's name contains the Japanese words for "tide" (潮), fitting the oceanic naming theme of Kairi and Naminé, and Aster tataricus (紫苑). According to Japanese floriography, Aster tataricus is used to mean "I won't forget you" or "remembrance". It is also revealed within the Secret Reports that her "original name" was "No.i", her ID as an experiment of the Replica Program. The "i" used here is in fact the imaginary number.

Kingdom Hearts 358/2 Days
A week after Roxas joins Organization XIII, Xemnas introduces Xion to the other members. After looking at the other members, she smiles up at Roxas, puzzling him. As Roxas departs for his first training mission, he spots Xion shyly watching him nearby, and Saïx formally introduces her to Axel and Roxas.

When Axel is sent to Castle Oblivion, Xemnas entrusts Roxas to look after Xion, who quickly bonds with him. She reveals her ability to wield the Keyblade to him, and looks after him when he falls into a coma for several weeks in conjunction to Sora being put to sleep to regain his memories. After discovering that Sora and Riku had slain all of the Organization members (except Axel) that were in Castle Oblivion at the time, Roxas, Axel, and Xion all begin spending more time together as per Roxas's suggestion and become fast friends, such as enjoying sea-salt ice cream together. After Xion asks Axel to be her friend, and he accepts, he stops seeing her as a doll, and begins seeing her as the black-haired girl that Roxas sees.

However, a series of events begin to split the trio apart: While DiZ and Naminé oversee the restoration of the sleeping Sora's memories (moving him from Castle Oblivion to Twilight Town), Roxas begins to experience the process for himself, and begins to ponder over how he is able to wield the Keyblade and doubt the Organization's motives; Axel is reprimanded by their superiors for placing his friendship with Roxas and Xion before the Organization's goals; and Xion is thrown into disarray after a confrontation with Riku, who questions who she is and why she wields the Keyblade, becoming torn between staying with her friends and leaving the Organization to merge with her true self as Riku suggests.

Xion travels with Riku for several days before being captured by Axel and brought back into the Organization. However Naminé's attempts to restore Sora's memories are soon halted when Xion starts absorbing them faster, causing Roxas to weaken while she becomes stronger, as Xemnas intended. Eventually, after being tricked into fighting Roxas by Saïx, Xion decides to take Riku's advice and leaves the Organization.

After her departure, Xion comes into contact with Naminé at Twilight Town's Old Mansion, questioning her own existence and the fate that will soon befall Roxas. She discovers that she is not a Nobody, but an imperfect Replica of Sora created as a fail-safe in case Sora and Roxas turned out to be useless to the Organization's plans. Naminé also reveals that as a memory being, once Xion returns to Sora everyone's memories of her will inevitably be forgotten. Furthermore, Naminé's attempts to restore Sora's memories not only affect Roxas, but Xion as well, stating why they both keep having memory relapses throughout the game. Xion accepts the facts, and decides to go back to Sora. Before she does, though, DiZ barges in with the news that an Organization member has followed her, in which Xion says she will take care of it, despite Naminé's protests, and heads out of the mansion.

It is Axel who has arrived, having finally tracked Xion down. Not only is Axel curious of Xion's motives, he is also given specific orders to capture her again, which would possibly convince Roxas to return to the Organization. Xion refuses, leaving Axel no choice but to accomplish his mission with full force, leading to a heated battle. Having defeated Xion, Axel brings her back to The World That Never Was, but soon faints from fatigue. Xemnas then steps out from the shadows and carries the unconscious Xion away to reprogram her to use the devices he had planted throughout the worlds.

Soon afterwards, Roxas finds Xion at the Twilight Town train station, and after she reveals her altered, Sora-like form to him, she explains that she has been compelled by Xemnas to absorb Roxas and become a "full" Sora, which would in turn prevent the real Sora from ever waking. It is explained in her Secret Reports that this is somewhat of a ruse - she knows that Roxas will disappear if she continues to exist, so she plans to force Roxas to absorb her, saving himself and thwarting Xemnas. She then transforms into a monstrous version of Sora using Xemnas's devices, and attacks.

During the battle, Roxas and Xion are transported to Wonderland, Halloween Town, and Agrabah, before returning to Twilight Town. In each world, Xion absorbs power from the "devices" that were placed there, which contain memories of Sora's battles in each world. After a long and grueling battle, Roxas manages to defeat her, while she regains her original appearance in his view. When done, he doesn't seem to recall who she is, though she assures him that he'll be better off now. Cradling her in his arms, Roxas shares an emotional conversation with her, during which she explains to him that she had no regrets for meeting him or Axel, reveals the true colors of the Organization to him, and pleads with him not to let Xemnas win before dying peacefully in his arms. Saddened, Roxas suddenly remembers her name and holds Xion's hand as her body crystallizes and disintegrates into nothingness.

Though Naminé states that everyone's memories of Xion will vanish when she does, Roxas, Riku, Xemnas, and Saïx manage to retain some memories of her into the next day. By then, Roxas has returned to the World That Never Was in order to set Kingdom Hearts free, which he hopes will reunite him with Xion. However, he is being stalked by a swarm of Neoshadow Heartless, as well as a determined Riku, who has arrived to capture Roxas to finish Sora's memory restoration. Riku looks down upon the Nobody, before Roxas starts his path up the skyscraper. Through him, Xion is able to throw the Oblivion Keyblade to Riku in order to tell him to stop Roxas before he can reach Xemnas, because she believes Roxas is not strong enough to face him yet. In turn, touching the Oblivion causes Riku to recall flashbacks of the time he spent together with Xion, putting him in shock for a moment.

When Roxas and Riku finish eradicating the Heartless, they turn on each other for a battle. By this time, it is a struggle for Roxas to even remember Xion's name, and all he knows about her is that he wants her back. While Roxas is able to knock Riku down first, Riku manages to stop Roxas once he removes his blindfold and transforms into Riku-Ansem. Unconscious, Roxas hears Xion talking to him through his mind, telling him not to be sad, as she has become one with him and Sora, and that soon Roxas will also join them. Despite the fact that memories of Xion have been forgotten by everyone, she tells him that she still has her own memories, so she doesn't mind that he has forgotten her, as she won't forget him or Axel. As Riku knocks him out, Roxas's last memories of Xion fade away.

Kingdom Hearts coded
In the Data Castle Oblivion, the data Naminé reveals to Data Sora and King Mickey that Xion is one of the people that, while gone, is still connected to Sora's heart.

Reconnect. Kingdom Hearts
After Aqua speaks with Ansem about Sora, Xion is sitting atop the Twilight Town clock tower and eating sea-salt ice cream with her friends (Roxas and Axel). Then, Xion and Roxas say Sora's name while watching the sunset together.

Appearance
Xion's Organization coat is similar to the one Roxas wears, with slightly pointed shoulders and closer-fitting sleeves. She also wears the more feminine, heeled boots that Larxene wears and the basic black gloves. Physically, Xion strongly resembles Kairi in her appearance from the first game, having virtually the same haircut (though Xion's hair is black and parted on the left side of her head rather than the right as it was on Kairi) and eye color (blue). She is roughly the same height as Roxas, albeit a bit shorter. As a result of her being crafted from Sora's memories, Xion's appearance is somewhat unstable and she transforms into Roxas (in his Black Cloak) and both Riku and Sora in their original appearances from the first game. Her appearance is also slightly different depending on who is looking at her, which is most noticeable when Xigbar sees her as Ventus.

During Roxas's battle with Xion, she dons armor which changes a number of times throughout the fight. Her basic form is a bizarrely-shaped suit that is predominantly silver and black, with some dull red armor near her waist, gold on her boots, and orange armored gloves. Xion's helmet sports two black spikes that jut out horizontally on either side and a large, red Nobody symbol on the faceplate, part of which forms something of a horn on the top of the helmet. In her first fightable form, Xion has large, skeletal, colorful wings and a huge, orange and red, intricately-shaped sword. In her second form, Xion loses her wings and grows to be about twice the size of Roxas, summoning a large, scythe-like weapon vaguely resembling the Decisive Pumpkin Keyblade or a Chimaera arm as a weapon.

For the third section of the battle, Xion transforms into a figure with four huge arms, decorated with elegant, gold, purple and red designs. She also has large blades instead of hands, resembling Kurt Zisa's own arms. Her main body is also slightly larger than normal during this part of the battle. In her final transformation, Xion grows to titanic size, about the same height as the Train Station tower. Her armor is now embroidered with numerous spikes and ribbons. She also gains two Keyblade-like, pink and silver weapons with the teeth in the shape of the Nobody symbol as well as Sora's signature crown's spot is replaced with a Nobody symbol.

Personality
First arriving at Organization XIII, Xion is a shy, secluded individual. When going on a mission with Roxas, Xion begins to open up to him, and later Axel. She does seem to express emotions due to her nature of existence, and is always happy to be with her friends. However, she is somewhat emotionally fragile, becoming deeply enraged with the right provocation. After finding out the origins of her existence, she also becomes deeply confused and lost. She has a strong sense of justice and generosity, seen in the way she willingly gave up herself to join with Sora. She resembles Kairi and Namine in the way that she fights to protect those she has come to care for.

Xion seems to take an interest in seashells. While Roxas was in a coma when Sora was put to sleep, Xion put a seashell on his bedside table every day he was asleep. In her nightmare on Destiny Islands, Roxas is in the dream and picks up a shell while whispering her name. After Xion was absorbed into Roxas, all that was left of her was a single seashell. This is likely a reference to how Kairi also had a liking for seashells.

Fighting Style
As Sora's Replica, Xion's fighting style as a playable character is very similar to his. After absorbing many of Sora's memories using the Organization XIII Devices, Xion is able to replicate Sora's Limits from Kingdom Hearts. However, Xion's movement is quite similar to Limit Form's, jumping back and stepping forward between attacks and slashing through the enemy in the finisher. Like Roxas, she thrusts with one hand and her finisher resembles the Vortex ability. Xion's Limit Break, Event Horizon, involves covering her Keyblade in an aura of Light and performing a devastating combo. Xion can also call down elegantly shaped pillars of light to attack nearby and far away enemies. Before Xion obtains the Keyblade herself, she is limited to simply shooting magic out of her hand, none of which is Light-based.

Once she obtains her Keyblade, Xion is very good at handling it, being able to fight with it using her right or left hand. Her boss battle depicts her using many powerful melee attacks she seemed to have inherited from Sora. She also uses light much more often during her boss fight, such as creating spiraling circles of Light that suck in the player, leaving them vulnerable to one of Xion's aforementioned physical attacks. She can also use a Light spell similar to Ragnarok, and can envelope her weapon in Light to make her other attacks even more powerful.

Weapon
As Roxas's Replica, Xion can wield the Keyblade. She wields her weapon fairly skillfully, being able to disarm Axel. Because Xion and Roxas are both part of Sora, they can both wield his Keyblade, even at the same time. Xion and Roxas can share keychains with each other, allowing them to use the same Keyblades and limit break in multiplayer mode.

It is notable that, when Xion runs with her keyblade, she grasps it with two hands instead of slinging it over her shoulder. This is similar if not identical to how Sora runs with his keyblade in Kingdom Hearts II.

Playing as Xion
In Kingdom Hearts 358/2 Days, Xion fights in the exact same manner as Roxas, acting as nothing more than a gameplay carbon copy. Like Roxas, she also has low, but even stats, which make her just as versatile as Roxas, able to specialize in any specific area. Xion's Limit Break, Event Horizon, is the same Limit Break that Roxas uses. She rapidly attacks around the field while her Keyblade is enveloped in light, slashing away at enemies with great speed and strength. During the Final Limit, Xion summons four thin pillars of light that quickly move in straight paths to the ends of the field, dealing heavy damage to any enemies in their path. Unlike Roxas, however, Xion is unable to Dual-Wield her Keyblades by using the Zero Gear and three ability units; her weapon will just revert to a Kingdom Key+ with this panel combination.

Quotes

 * "My Keyblade is not a sham! What gives you the right to say that?"
 * "Is it that I'm not supposed to exist?"
 * "I want...I want to be...with you two."
 * "I'm sorry, but... I can't go with you. It's my friends - they need me. And I need them, too."
 * "I've decided that I have to go back to where I belong." 
 * "Please don't hold back, Axel. Promise."
 * "I belong with Sora. And now, I am going back... to be with him."
 * "Roxas... I need you... to do me a favor. All those hearts that I've captured... Kingdom Hearts...  Set them free."
 * "Goodbye, Roxas.. See you again. I'm glad... I got to meet you. Oh... and of course, Axel, too. You're both my best friends. Never forget. That's the truth."
 * "Roxas, don't be sad. I came from you and Sora. I am you... the same way that I am Sora. You'll forget me, but the memories themselves will never go away. Memories of you and me will always be together... forever, inside him."

Trivia

 * Xion's name was coined by Tomoco Kanemaki, one of Kingdom Hearts 358/2 Days's scenario writers. Tetsuya Nomura took a liking to it and notes that it has many meanings.
 * Xion is the second female character that is playable in the Kingdom Hearts series; after Larxene.
 * After Roxas joined with Sora, information on the five Organization members that were eliminated in Castle Oblivion is added to Jiminy's Journal, due to Roxas's memories of them. Xion is not mentioned because all of the memories of her had been completely erased, as seen in the cutscene after battling Riku in Kingdom Hearts 358/2 Days.
 * Xion was voted "Best New Character" for the 2009 Nintendo Power Awards.