The Dark Hero [Highschool DXD x Male Ryuga Reader]

Before the Dark Dragon rised, several fallen angels discovered a powerful sacred gear within a young grown child, waiting to use this blue haired boy for their benefits, they take him to Kuoh Town for their new leader, Rias.

However, little does he know that he holds the powerful Ryuga deck to defeat the several evil creatures known as Mirror Monsters, who are also known as the world that exist behind the mirrors the sacred gear that holds the source of their power, the advent decks.