With his massive demon legions, the Demon Lord Satan begins to invade the continent of Ente Isla, striking dread into the hearts of mankind. However, while beginning on this heinous journey to conquer the continent, Satan's efforts are thwarted by the hero Emilia, leading Satan to flee via a dimensional portal only to arrive in the human realm. The demon, together with his devoted general Alsiel, is stuck in modern-day Tokyo and pledges to return and complete his dominion of Ente Isla—if they can find a way back! In a world without magic, Satan disguises himself as Sadao Maou, a human, and begins working at MgRonald's, a local fast-food restaurant, to make ends meet.