Devils and Realist

William, a member of an aristocratic family, returns home after his uncle's business fails, leaving them financially strained. In search of assets to sell, William and his family's butler scour the estate and discover an underground room left by one of their ancestors. The room contains a magical seal, which William inadvertently uses to summon a devil named Dantalion, who claims William is a "designator" able to choose the ruler of the demon world.