Vanitas

Vanitas is a Keyblade wielder and one of the primary antagonists in Kingdom Hearts Birth by Sleep. He is the apprentice of Master Xehanort. Created by Master Xehanort, Vanitas is the embodiment of the extracted darkness from Ventus's heart. Vanitas's birth sparked the threat of the Unversed.

Kingdom Hearts Birth by Sleep
A mysterious figure with ties to Master Xehanort.
 * The Masked Boy

He warned Ventus that Terra was in some kind of danger, but disappeared before explaining any further.

''A mysterious boy who hides his face behind a mask. He has ties to Master Xehanort.''
 * Vanitas

Vanitas warned Ventus that Terra was in some kind of danger, but disappeared before explaining any further.

Kingdom Hearts Birth by Sleep
Four years before the events of Kingdom Hearts Birth by Sleep, Ventus served as Master Xehanort's apprentice. The Keyblade wielder was sent to the Keyblade Graveyard, where he was forced by his master to face several Heartless. Ventus refused to use his darkness, and was knocked unconscious. Master Xehanort then proceeded to use his Keyblade to unlock Ventus's heart, extracting the darkness within and resulting in an orb of dark energy forming into a young boy in a mask who is then given the name "Vanitas" by Master Xehanort. The dark enigma is also the source of the Unversed, as well as a key component in Master Xehanort's plans.

After Master Xehanort views the battle between Terra and Aqua as part of their Mark of Mastery exam, he leaves the room to find a hidden Vanitas awaiting him. The two converse about Ventus, and Vanitas claims that Ventus's performance was weak, and he still needs to "break that loser in." Master Xehanort instructs him to do so somewhere else as he needed to keep up appearances. So Vanitas decides to give Ventus an "incentive" to leave home. Vanitas later appears before Ventus in his room, speaking of Terra being a different person, and that Ventus should follow him before it's too late. Ventus becomes very defensive, saying that Vanitas does not know the first thing about Terra, and that they will always be friends. Vanitas simply mocks his friendship with Terra, telling him to grow up and vanishes into a corridor of darkness, claiming that unless Ventus sees it for himself and looks beyond his "own little world", he will not know the truth.

After his first few ventures throughout the worlds, Ventus spots Vanitas in space and is lured to the Keyblade Graveyard. Ventus interrogates him about what he meant about Terra being a different person. Vanitas simply reiterates what he said before, that Terra will be gone forever, and challenges him to a duel, intent on testing his power and revealing for the first time he is a Keyblade wielder. Despite Ventus's best efforts, Vanitas gains the upper hand mid-way, knocking Ventus down. Vanitas then prepares to eliminate Ventus for being at such a low level of power, deeming the boy too worthless to be of use, but before he could do so, Mickey Mouse appears, healing Ventus. Mickey Mouse and Ventus then proceed to fight Vanitas, who simply shrugs off the fight and leaves yet again upon his defeat, claiming that Ventus is on "probation".

After the battle against the Trinity Armor in Radiant Garden, Ventus, Terra, and Aqua go their separate ways after an argument. Vanitas appears to Aqua and approaches her while in the central square, taunting her by calmly inquiring about Ventus and if he has gotten stronger. When Aqua asks what he means, Vanitas, in a more hostile tone, states that he is asking the questions as he claims he will be the only one who will walk away alive, and attacks, the two fighting a vicious battle with Aqua as the victor. After the duel, Aqua attempts to remove Vanitas's helmet, but the dark enigma startles her with an insane laugh. He then compliments her skill and congratulates her on her victory, making an ambiguous comment about her being his backup plan, revealing that it was all a ruse to test her strength. Ventus overhears Vanitas's last few words to Aqua, returning to her side just as he leaves in another corridor of darkness.

While in Neverland, Vanitas encounters and kidnaps Mickey Mouse on Master Xehanort's orders. Though the fight is not shown, it is clear Vanitas won. The villain later crosses paths with Aqua again, this time with Ventus's cherished Wooden Keyblade. Vanitas cruelly mocks Aqua for playing treasure hunter with the Lost Boys and snaps the toy weapon in two, claiming that Ventus has outgrown the toy, much to Aqua's anger and horror. Vanitas also claims that he has outgrown his need for Aqua as a backup plan and prepares to fight, intent on eliminating her. Aqua, outraged by the act of cruelty and further enraged at the thought of Ventus being in danger, battles the dark enigma once again, soundly defeating him and knocking him out cold. The battle leaves Aqua exhausted, as Vanitas then disappears through a corridor of darkness.

Vanitas encounters Ventus again in Destiny Islands, after the latter is thrown through a portal summoned by Terra. Ventus initially tells Vanitas that he is through with him. But Vanitas simply tells him that since they are equal in power, they can fuse together to create the χ-blade. Ventus refuses, claiming that the χ-blade cannot be created if he does not fight. Vanitas, though slightly angered, remains unfazed, responding only by coldly stating that Ventus was once "too broken to talk back." Then, in a series of flashbacks, Vanitas explains his birth from the darkness in Ventus's heart, and how he took his place as Master Xehanort's apprentice. This causes Ventus great pain in regaining his memories. Vanitas challenged Ventus to come find him in the Keyblade Graveyard, the one and only place where the x-blade can be forged, where he threatens to "choke the life" out of Terra and Aqua and callously wonders how long Ventus will "play the pacifist." Ventus, haunted by Vanitas's deranged threats, and determined to end this once and for all goes to the Keyblade Graveyard.

When Terra, Ventus, and Aqua approach their final battle with Vanitas and Master Xehanort at the Keyblade Graveyard, intense battles ensue. The two villains meet up with the trio, and after Master Xehanort explains his plans, the trio armors up and Terra quickly charges towards them. Master Xehanort intervenes, however, blocking Terra's path with massive rock formations. As Terra continues to pursue Master Xehanort, Vanitas goes after Aqua and Ventus, riding on a cloud of Keyblades Master Xehanort created. The two fight valiantly against the dark apprentice, but not before Vanitas returns to Master Xehanort's side after Ventus is frozen. He battles Terra alongside Master Xehanort, who later commands Vanitas to go after Ventus and Aqua again.

Vanitas attacks Aqua from above, knocking her unconscious, and prepares to impale her through the chest while Ventus lies helpless and frozen. Ventus summons all of his willpower, however, and breaks out of the ice to face Vanitas in battle, defeating him once again. Vanitas compliments Ventus on his skill and finally reveals his face, explaining himself to be the source of all Unversed. Vanitas then summons several Flood Unversed to restrain Ventus as he proudly explains his plan: to spread the Unversed across the worlds, so Ventus could leave his home and grow strong enough to forge the χ-blade. He then forcefully integrates into him. In a burst of light, Vanitas and Ventus are transported to the Dive to the Heart. Ventus's pillar now hosts a picture of Vanitas alongside his own. Vanitas wields an incomplete version of the χ-blade.

Vanitas claims their fusion was incomplete, and they only managed to make a fraction of the χ-blade. He then tries to fuse with Ventus once again, but Ventus refuses, vowing to defeat Vanitas and destroy the χ-blade. The dark apprentice simply laughs, confident in the fact that they both know that if the χ-blade is destroyed, Ventus's heart would vanish forever. However, Ventus rebukes him, saying he will fight for his friends no matter what, even if the price is his heart, despite Vanitas's mocking of his reason to fight. The two Keyblade wielders then begin a final showdown in the Dive to the Heart.

As Ventus battles Vanitas in their Awakening, Aqua and Mickey are forced in the Keyblade Graveyard to battle a sort of Ventus-Vanitas fusion, which is Ventus's form with Vanitas's golden eyes and bodysuit. Ventus-Vanitas summons the completed χ-blade, and exclaims with psychotic glee that he plans to unlock Kingdom Hearts so the worlds can be connected and the legendary Keyblade War can begin again, and attacks the duo. As Aqua defeats her possessed friend and destroys the χ-blade, Vanitas's metaphysical battle with Ventus comes to an end after he shatters the pillar on which they were fighting. Vanitas fades out of existence, taking all Unversed in existence with him and relinquishing his control over Ventus. Unfortunately, the victory is bittersweet, as Ventus loses his heart and falls into a coma in the process.

Appearance
Vanitas wears a black and red organic-looking bodysuit, which is quite similar to Riku's Dark Mode from Kingdom Hearts and Kingdom Hearts: Chain of Memories. He wears a silver helmet covered with dark glass, hiding his face from view. Just before he possesses Ventus, he unmasks himself, revealing that he looks identical to Sora, although he possesses golden-yellow eyes, black hair, paler skin, and a more muscular build. In an interview with Tetsuya Nomura, it is revealed that this similarity is due to Sora's heart connecting with Ventus near the beginning of the game, and had anyone else connected with Ventus's heart, Vanitas would look like that person.

His appearance before Ventus's connection with Sora has yet to be revealed. He normally wields his personal Keyblade, the Void Gear, that is colored primarily in red and black, with two blue eyes like the Soul Eater, Way to the Dawn, Chaos Ripper, and Master Xehanort's Keyblade, but near the end of the game he gains the χ-blade, and when he fuses with Ventus, he also alters Ventus' body to accommodate his yellow eyes and bodysuit.

Personality
As a being created from the purest of darkness, Vanitas is proud, cunning, cruel, and pure evil. The lives of others, including that of even Master Xehanort, hold absolutely no value to him, and he shows no remorse for his actions. As a pragmatist, he will strike without a moment's thought or warning, as seen when he ambushes Aqua in the Keyblade Graveyard and attempts to eliminate her. Despite his loyalty to Master Xehanort, he has disregarded his orders on occasion; for example, he attempts to eliminate Ventus after defeating him in their first battle despite full knowledge that Master Xehanort needed Ventus alive for his plans. For the most part of the game, he is shown to be cool, calm, and collected, never breaking his calm until near the end of the game. He appears to be quite intelligent, as seen in his quotes. He is also shown to be uncaring, having not the slightest sympathy for anyone but himself, as seen in his frequent criticizing of Ventus's friendships with Terra and Aqua, and when he callously breaks Ventus's wooden Keyblade, and his constant referring to Ventus as an "idiot," in addition to forcing Ventus to fight him by threatening to kill Terra and Aqua. He can also be overconfident and arrogant at times; in his first fight with Aqua, he claims that he will be the only one that will walk away alive, and when fighting Aqua for the final time, Vanitas boasts that Aqua was just "wasting her energy" trying to stop him, and when fighting Ventus for the final time, he laughs maniacaly when Ventus declared he would defeat him and destroy the χ-blade. His overall personality is in an extremely stark contrast to Ventus and Sora, and by extension Roxas and Xion, who are valiant, value friendship, and possess heroic qualities.

Vanitas also appears to be somewhat insane, judging by what has been shown in-game. The most prominent examples include his bursts of maniacal laughter when Aqua tried to unmask him and when Ventus declared he would defeat him and destroy the χ-blade, and his explanation to Aqua and Mickey about what he plans to do with the χ-blade and Kingdom Hearts after possessing Ventus, the latter of which he does with a crazed smile on his face.

Abilities
Vanitas is, to say the least, a skilled and extremely aggressive opponent, showing a mastery in both dark magic and wielding the Keyblade. He is swift and agile, able to perform complicated and nearly impossible acrobatic feats such as jumping off of a high cliff while still landing on his feet, and even riding a cloud of flying Keyblades. He can teleport behind opponents at high speeds to launch attacks while leaving after-images of himself to confuse them. He is also able to combine physical combos with magic such as attacking from above and causing a large pillar of ice to shoot out of the ground, or attacking opponents from below while bombarding them with fireballs. He appears to have superhuman endurance, surviving each of his battles while taking little to no bodily damage. Vanitas also seems to possess superhuman strength; while possessing Ventus, he is able to shatter Ventus's metaphysical Dive to the Heart pillar with a single strike and create a gust of wind powerful enough to send Aqua and Mickey flying with a single swing of his arm. It is most likely that these actions were made possible only through the χ-blade, which Vanitas wielded on both occasions. Vanitas is also a difficult opponent to fight in close combat, as he can quickly counterattack if struck multiple times, making him very dangerous. He also demonstrates the ability to levitate.

While Vanitas acts based on his own desires, it appears that Master Xehanort can summon him at will. Vanitas's arguably most dangerous and destructive ability, however, is the power to create and control the Unversed. As he was born from the purest form of darkness, Vanitas can manipulate negative emotions and spawn them as Unversed. Vanitas can absorb the negativity of any defeated Unversed, able to summon them again if needed.

Weapon
Vanitas wields a Keyblade known as the Void Gear, and has a battle pose that is very similar to Riku's stance. The Keyblade can be summoned at will, appearing in Vanitas's hand in a flash of purple flame. The Vanitas Remnant also wields a monochrome version of this Keyblade.

When fused with Ventus, Vanitas gains the ability to wield the most powerful Keyblade of all, the χ-blade. This weapon multiplies his initial strength and attack range a great deal. Vanitas shows great skill in wielding both the incomplete and finalized versions of the χ-blade, able to perform strong combos and powerful desperation moves.

Trivia

 * After his first spoken line, Nomura made a joke saying that he was to voice Vanitas. Nomura also stated in another interview that Vanitas's identity was familiar and perhaps also shocking. It was later revealed that Vanitas was voiced by Miyu Irino, the Japanese voice actor for Sora. According to Tetsuya Nomura, Irino had said for a while that he wanted to play an evil character, and Nomura jokingly stated he sort of got carried away with it.
 * Vanitas's name is derived from the Latin word for "Vanity" or "Emptiness", and was chosen for its meaning, that it sounded similar to "Ventus", and that it was a written pun on "Sora" in Japanese.
 * The Kingdom Hearts Birth by Sleep Ultimania refers to Vanitas as the Masked Youth (仮面の少年).
 * Out of all the antagonists to appear in the series, Vanitas has been fought in the most boss battles, a total of seven battles in all.