Dean Winchester/Castiel
Set either in the present season, or a mutually agreed upon time in the past, Castiel is sent to the Winchesters, completely human. His Grace was ripped away from him and the only people he can rely on to teach him to be human are the Winchesters and Bobby. Dean and Castiel grow closer while Castiel explores that being human isn't so terrible and there are things he enjoys about it.
I was kind of thinking that Castiel might be asexual, with no real sexual attraction to anyone, as there is a difference between romantic and sexual attractions, so when he and Dean grow clsoer, Dean has to deal with the frustration of no sex, which he's not used to, and Castiel is struggling with this idea that he's not like all the couples he sees in life and on television. This is negotiable.
I play over AIM and I'm not looking for book-length replies.