I really shouldn't have to say this...
When writing crossovers, be sure your canons mesh well. Specifically, be sure that crossing worlds would be allowed, Heartless would be believable--that sort of thing. Really, I'm all for crossovers, and I like it when somebody manages to take two fandoms that don't look like they'd mesh together too well (take some CSI crossovers, for instance, where they might cross with Harry Potter) and make them work.
But honestly? I don't think there's any way you can justify Kingdom Hearts/Bones.
But honestly? I don't think there's any way you can justify Kingdom Hearts/Bones.