As Sora begins his journey to regain his power, Yen Sid and the others turn their attention to finding the three lost Keyblade wielders: Ventus, Terra, and Aqua. The team has their work cut out for them, but luckily, King Mickey has a lead—he chanced upon Aqua once before in the Realm of Darkness! Just what exactly happened to Aqua when she vanished…?