It's really the afterlife, if you don't believe me try jumping off a rooftop. Someone in charge of it.. well, that's a tough call. It depends on how "in charge" you want to get. There's another man who acts as a programmer but he's definitely not a good guy-- he can manipulate the NPCs and tell them to completely wipe everyone's memories and make us like them if we aren't careful. Then there's Naoi, who's in charge of the student council. And me, of course, the leader of the Shinda Sekai Sensen, afterlife battlefront. The closest thing to "overall leader" you're going to get is God, but I've been trying to find my way to him for years without success.