Vanitas

Vanitas is Chernabog's demonic human son, forged by an unholy union between Maleficent and himself, and heir to the Dark Spawn throne after Malefor. In the KH series, he is the second apprentice of Master Xehanort. Created by Master Xehanort, Vanitas is the embodiment of the extracted darkness from Ventus's heart and the progenitor of the Unversed.

Kingdom Hearts Birth by SleepEdit

 * "Empty creature from Ventus riven... to you, the name Vanitas shall be given."
 * —Master Xehanort, upon Vanitas's creation

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 in an attempt to forge the χ-blade. Ventus was unable 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 and try to help 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 "tiny world," he will never know the truth.

Vanitas then travels to different worlds, spreading his Unversed across them in hopes of making Ventus strong enough to forge the χ-blade.

After his first few ventures throughout the worlds, Ventus spots Vanitas in the Lanes Between 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 easily outmatches Ventus, gaining the upper hand mid-way, and knocking him down. Vanitas then prepares to eliminate Ventus, deeming the boy too worthless to be of use, but before he could deal the final blow, Mickey Mouse appears, healing Ventus. Mickey then reprimands Vanitas for using his Keyblade to bully others, and the two 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, the ensuing argument forces Terra, Ventus, and Aqua to go their separate ways. While Aqua is in the Central Square, Vanitas appears, 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 that between the two of them, 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 unmask Vanitas while he is unconscious, but the dark enigma quickly recovers, startling 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 returns to Aqua's side just as he leaves in another Corridor of Darkness.

While in Neverland, Vanitas encounters and kidnaps Mickey on Master Xehanort's orders to use Mickey as bait to lure Ventus back to the Keyblade Graveyard. 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 "kiddies", proceeding to tell her that, with Ventus's newfound strength, he has "outgrown" the toy, and then snaps it in half, an act that both enrages and horrifies Aqua. Throwing the pieces aside, Vanitas also claims that he has outgrown his need for Aqua as his backup plan and draws his Keyblade, intent on eliminating her. Aqua, outraged by the act of cruelty and at the thought of Ventus being in danger, calls Vanitas a freak and battles the dark enigma once again, soundly defeating him and knocking him unconscious. Aqua, believing she has finally finished Vanitas, and exhausted by the battle, passes out, as a revived Vanitas takes the opportunity to escape once again.

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 he is strong enough, Ventus can join with him to forge the χ-blade. Ventus refuses, claiming that the χ-blade cannot be forged 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 the ensuing flashback, 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 then gives Ventus a reason to fight, challenging the boy to come find him in the Keyblade Graveyard, the one and only place where the χ-blade can be forged, where he threatens to kill Terra and Aqua to see how long Ventus will "play the pacifist." He then disappears into a Corridor of Darkness. 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 for the χ-blade, 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 before the latter freezes Ventus. 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 with a devastating blow, and prepares to impale her through the chest while Ventus lies helpless and frozen. Ventus summons all of his willpower, however, and thaws 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. Glowing with dark energy, Vanitas then summons several Flood Unversed to restrain Ventus as he proudly explains his plan: to spread the Unversed across the worlds, in hopes of luring Ventus from home and making him 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 union was incomplete, and they only managed to make a fraction of the χ-blade. He then tries to join 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 and destroy both him and the χ-blade 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 shared mind, Aqua and Mickey in the Keyblade Graveyard are attacked by a Vanitas-possessed Ventus. Ventus-Vanitas summons the completed χ-blade, and tries to attack Aqua, only for her to be saved by Mickey. He then goes on to explain that he plans to unlock Kingdom Hearts so the worlds can be connected and the legendary Keyblade War can begin again. Aqua, sick of Vanitas's nonsense, confronts him in battle one last time. 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 is completely destroyed, taking all Unversed in existence with him and relinquishing his control over Ventus. Unfortunately, it is a pyrrhic victory, as Ventus loses his heart and falls into a coma in the process.

Role in the series
But that wasn't the end of the demon boy by a long shot. In fact, Chernabog decided to resurrect his son in order to provide the Dark Spawn Lords with a future king instead of that failure of a servant, Malefor.