Kiyone Hyoudou is the older twin sister of Issei Hyoudou and unknown to him, is a fallen angel. After Issei is killed by Raynare and reincarnated as a devil, Kiyone vows to protect him in secrecy from everyone who would dare cause him harm. If your sister was a fallen angel and you were a devil, what would you do? Will follow the anime, manga maybe later. Minor times Issei is OOC.