Instilling terror within mortal hearts, the Demon Lord Satan sets out to conquer the realm of Ente Isla with his formidable demonic armies. However, his ruthless campaign is thwarted by the hero Emilia, compelling Satan to hastily escape through a dimensional portal, landing him in the human world. Stranded in modern-day Tokyo alongside his loyal general Alsiel, Satan resolves to find a way back and resume his quest for dominion over Ente Isla.
Devoid of his magical powers in this unfamiliar realm, Satan adopts the human identity of Sadao Maou and secures employment at MgRonald's, a local fast-food establishment, to make a living. Realizing that conquering Ente Isla alone is not sufficient, he sets his sights on climbing the corporate ladder and becoming the ruler of Earth, one satisfied customer at a time.