Once upon a time, humanity lost a war against the demons led by four demon lords, and survived on what little land was left under the protection of the seven holy swords.Humanity continues to live its life fighting against the attacking demons, armed with numerous ``imitation holy swords'' made in imitation of the seven sacred swords left behind by the goddess.This is the story of Roy, a boy who is branded as a ``fallout'' in a world where the holy sword is the ultimate, and the strongest and worst demon lord who is sealed away by four demon lords and saves the world.