Ventus (DwtDS)

Ventus is a Main Character in Deal with the Devil Series and one of the three Main characters of Kingdom Hearts Birth By Sleep, following his entrapment in a magical Coma generated from the shattering of his and Vanitas's hearts following the Destruction of the incomplete χ-blade, for ten years Ventus slept while the remaining Darkness that was once called Vanitas and its own shattered heart preserved his body and mind.

Pre-Birth By Sleep
Ventus's Homeworld is largely unknown but at some point Master Xehanort apprenticed Ventus under his care and allowed him to "inherit" his Keyblade, Ventus thereby came to wield a Keyblade of his own and began training under Master Xehanort in the usage of wielding his Keyblade, given the unique heart that the boy had the quickly maddening and fallen Keyblade Master used him as part of his grand experiment.

Master Xehanort began training Ventus brutally, including the summoning of Heartless from the Realm of Darkness to battle the boy and to attempt to force him to use the latent Darkness within his heart as a weapon, the boy refused however to use the Darkness to empower himself and was defeated. Xehanort tore the pure darkness from Ventus's heart leading to the creation of Ventus's opposite: Vanitas, but feeling a moment of pity for the boy provoked Xehanort to take him to his own homeworld, where he was to be left to die in peace.

Fate would have other plans however as Ventus pulled through from his weakened state but lost his memories as Xehanort's apprentice as a result, seeing the light that could be kindled with Ventus, Xehanort took Ventus to Master Eraqus to complete his training. He continued to train for many years, alongside friends and fellow apprentices Terra and Aqua, since that day.

Trivia

 * Ventus is Latin for "Wind".