The Demon Lord Satan and one of his generals, Alciel, escape the world of Ente Isla through a gate to modern Tokyo, Japan after being confronted by the Hero Emilia and her companions. However, due to the lack of magic in the modern contemporary world, both Satan and Alciel change into forms representing what they would look like if they were human. In order to survive, Satan takes a part-time job in a fast food restaurant named MgRonald while Alciel serves as his houseman. One day, Satan, who now goes by Sadao Maō, meets a girl who is actually the Hero Emilia, who now goes by Emi Yusa. The story then unfolds and explores the personalities of each of the characters and their moral values. More characters show up from Ente Isla and they too face the new world dilemmas, often comically.