"They're... monsters, kind of. They come from the darkness in people's hearts. And they're attracted to it. And when you lose your heart you become one, too." Sora had spent a few minutes as a Heartless that way. A pretty weak one, too, which wasn't all that surprising. "People with dark hearts can control them, for a while, sometimes. 'Til they get consumed by them, which even somebody who does it said always happens eventually." After a moment, in fairness, Sora added, "Hook was scared of his, of what they'd do to him. He didn't give'em orders, he just... used'em like walking the plank. Which only worked when it wasn't me. So there is that."