Blue Drop: Tenshi no Bokura

Blue Drop: Tenshi no Bokura's main protagonist is Shouta, a regular high-school student. At the beginning of the story, Shōta is met by a girl who asks him to have sex with her. Not much time passes until Shouta finds out this girl is actually Kenzou, his former-male best friend, who has been transgendered by the Arume and commanded to get pregnant.