Yūichirō Hyakuya 「百夜 優一郎, Hyakuya Yūichirō」 is the main protagonist of the fanfiction Highschool: Devil X Seraph, and the Owari no Seraph series. He is a member of Rias Gremory's peerage, and in turn, apart of the Occult Research Club. He, along with Mikaela Hyakuya, possesses the "Seraph" gene, which is relevant to the forbidden taboo and the focal point of the story, "Seraph of the End."