Does he have a body at all then? If not, I wonder why he stays here.

[After all, with no body there's no need for food or oxygen and gravity is no object. Someone like that could just leave if they wanted to. Of course, Setsuna's in no great hurry to leave, so maybe this friend has a purpose of his own as well.]

I think they were always possible, the planet just forced us to look at things differently and realize the possibilities. An invisible being still makes more sense than a ghost, though.