Koiochi Outsider

Tenchika Yuushin, a member of the Angel Clan, infiltrates a high school in order to marry his beloved fiancé, Seiei..! However, when he reunites with Seiei after a long time, he finds that Seiei has completely changed from the child he was in his youth, becoming a dark, chuunibyou-obsessed gothic beauty! Moreover, it seems that Seiei is infatuated with something other than Yuushin, so Yuushin, feeling uneasy, follows him and finds him having a suspicious rendezvous at a dubious base of operations called the Dark Club. Yuushin is distraught that his beloved Seiei has fallen for his arch-enemy, the demon, but as they live together in the dorm, he is appointed as Seiei's "butt duty"--? ]