Due to an accident, Zane arrives in another world and is reborn as the son of the Demon Lord. In the vast and dark realm, he becomes the master of the dungeon, the successor to the Demon Lord. He faces the demons coveting the throne of the Demon Lord, monsters lurking in the depths of the earth, adventurers roaming around for treasures and legends, as well as knights coming from the surface to fight for justice. Under ancient oaths and banners, Zane will wield his scepter from the deep, dark underground to bring unprecedented change to the world.