Unfortunately that's because we've yet to learn much of them. The "Heartless" are physical embodiments of Darkness, so far as I can tell. They can take many forms, and spring out of shadows. As for the Darkness and what might control it...



I don't know. And, as far as I'm aware, no one else does either. Fighters from other worlds are unable to banish Darkness and Heartless, and we've been told that only a special blade can do as much. I've been here for months and it's disheartening, even to me.