Vanitas

Vanitas is a character and one of the primary antagonists in Kingdom Hearts Birth by Sleep. He is the sole apprentice of Master Xehanort, the game's main antagonist. Vanitas is from the darkness of Ventus's heart extracted by Master Xehanort to further his evil plan. Vanitas's birth sparked the threat of the Unversed.

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 lost the battle, and was knocked unconscious. Master Xehanort then proceeded to use his Keyblade to unlock Ventus's heart, resulting in an orb of dark energy forming into Vanitas. 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 Master Qualification 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 "not even close", and he still needs to "teach him some discipline". Vanitas later appears before Ventus in his room, speaks of Terra no longer being himself, to which Ventus denies saying he and Terra are connected. Vanitas simply calls his friendship with Terra stupid and vanishes into a corridor of darkness, claiming that unless Ventus sees it for himself, he won't know the truth.

After his first few ventures throughout the worlds, Ventus spots Vanitas in space and is led to the Keyblade Graveyard. Vanitas approaches him, speaks of Terra losing his identity again, and challenges him to a duel, revealing for the first time he is a Keyblade wielder. Vanitas gains the upper hand mid-way, knocking Ventus down. Vanitas then prepares to kill Ventus for being at such a low level of power, but Mickey Mouse later appears, healing Ventus. The two then proceed to fight the dark enigma, who leaves yet again upon his defeat claiming he will watch over him a while longer.

After the fight, Mickey's Star Fragment sends Ventus and Mickey both to Radiant Garden. There he reunites with his friends to tackle a massive Unversed, but afterwards Terra, Ventus, and Aqua go their separate ways. While Aqua stays behind to contemplate, Vanitas appears and approaches her, taunting her by inquiring about Ventus and if he's gotten stronger. When asked what he means, he rudely says that he's asking the questions and attacks, the two fighting a vicious battle. After the duel, Aqua attempts to remove Vanitas's helmet, but the dark enigma startles her with an insane laugh. He then complements her skill, making an ambiguous comment about her being his plan B, and finishes it by saying "be a good girl and get stronger". Ventus overhears Vanitas's last few words to Aqua, returning to her side just as he leaves in another corridor of darkness. Vanitas later crosses paths with Aqua again in Neverland with Ven's cherished Wooden Keyblade. The dark enigma cruelly snaps the toy weapon in two, claiming that since Ventus has gotten stronger, he no longer needs it thus Vanitas no longer needs her as his plan B. He battles Aqua once again. Leaving Aqua exhausted and enraged at the thought of Ventus being in danger, but just as soon as he had appeared, Vanitas vanishes yet again in a dark corridor.

Vanitas encounters Ventus again in Destiny Islands, after the latter is thrown through a portal summoned by Terra. Vanitas tells him that since they are equal in power, they can fuse together to create the X-Blade. Ventus refuses, claiming that if he doesn't fight, the X-Blade cannot be created so he won't fight. Vanitas angrily says that he is pretty defiant for a "cast off shell". 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 vanishing as Ventus flees the world, but not before the villain gives Ventus an "invitation" to the Keyblade Graveyard where he tells him he will see Terra and Aqua fight for the final time, and callously wonders if Ventus will just watch without batting an eye.

When Terra, Ventus, and Aqua approach their final battle with Vanitas and Master Xehanort at the Keyblade Graveyard, intense battles ensue. The two darklings meet up with the Keyblade wielders, Terra charging 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. The two fight valiantly against the dark warrior, but not before he 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 the final blow while Ventus lies helpless and frozen. Ventus summons all of his willpower, however, standing and facing Vanitas in battle again. The dark enigma reveals his face, revealing himself to be the source of all Unversed, and that he spread them across the worlds so Ventus could grow strong enough to form the X-Blade while summoning many Unversed to hold Ventus down as he forcefully integrates into him. In a burst of light, Vanitas and Ventus are transported to the Awakening, Ventus's pillar now hosting a picture of Vanitas, as well. Vanitas wields an incomplete version of the X-Blade.

Vanitas claims their fusion was incomplete, and they only managed to make most of the X-Blade. He then tries to re-integrate into Ventus once again, but Ventus refuses, vowing to defeat Vanitas and destroy the X-Blade. The dark enigma simply laughs, confident in the fact that they both know that if the X-Blade is destroyed, so will be Ventus' heart. But Ventus rebukes him, saying he will fight for his friends no matter what, even if the price is his heart. Vanitas mockingly asks "So its the whole for my friends' sake thing again?". Ventus says that a dark being like him could never understand friendship, and finishes his statement by saying "My friends are my power!", and the two keybearers face off for the final time.

As Ventus battles Vanitas in their Awakening, Aqua and Mickey are forced in the physical world to battle a sort of Ventus/Vanitas fusion, which is Ventus's form with Vanitas's golden eyes and bodysuit. Vanitas/Ventus summons the completed X-Blade, and exclaims with psychotic glee that he plans to unlock Kingdom Hearts and restart the legendary Keyblade War. He then attacks the duo. As Aqua defeats her possessed friend and destroys the X-Blade, Vanitas's metaphysical battle with Ventus comes to an end after they shatter the pillar on which they were fighting, with Vanitas fading 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. It's revealed that his face is identical to Sora's face, although he possesses golden-yellow eyes, black hair, and paler skin. 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. He normally wields a Keyblade that is colored primarily in red and black, with two blue eyes like the Soul Eater, Way to the Dawn, Chaos Reaper, and Xehanort's Keyblade, but in the final chapters, he gains the X-Blade, and also fuses with Ventus, resulting in him looking like Ventus wearing the dark suit.

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, he shows no remorse for his actions, and as a pragmatist, he would strike without a moment's thought or warning. He has disregarded his master's orders on occasion, such as when he attempts to kill Ventus, despite the fact that doing this would interfere with Xehanort's plans. 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.

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 teleport behind opponents at high speeds to launch attacks. Able to combine physical combos with magic, he appears to have super-human endurance, surviving each of his battles while taking little to no damage.

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. All defeated sentiments return to him, able to be summoned again if needed.

Weapon
Vanitas wields a very unique Keyblade, his battle pose very similar to Riku's. The Keyblade can be summoned at will, appearing in Vanitas's hand in a flash of purple flame. Vanitas's Sentiment 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 X-Blade. This weapon multiplying his innitial strength and attack range a great deal, Vanitas shows great skill in wielding both the incomplete and finalized versions of the X-Blade.

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."Tetsuya Nomura: I wanted to give him a name that meant 'empty', and so I looked for something that would be appropriate. When I was searching I found a word that meant 'emptiness' in Latin, 'Vanitas'. It looked a lot like Ventus's name, and in Japanese it has the kanji for 'sora' in it, so I thought it was perfect. Of course in Vanitas's case it doesn’t mean 'sora [sky]' but 'kara [empty]' [These two words are written with the same kanji, but are said differently and have different meanings.]"
 * Only Master Xehanort and Ventus have seen Vanitas's face.
 * The Kingdom Hearts Birth by Sleep Ultimania refers to him 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.