I remember watching this anime... It's been bugging me and I can't remember what it's called, hopefully someone can help me. What I remember is, the main guy catches a girl falling from another floor and she weighed nothing and then she later explains that she lost her weight and the boy tells her he can help her get it back or whatnot. I think this would be a dead giveaway. I don't think this was a plot driven anime, it was pretty random.