Based on Satoshi Wagahara's novel series of the same name, the series follows the Demon King, who was beaten by the hero Emilia and along with his trusty general, they hastily retreat to a parallel world... only to land in modern day Tokyo! Now lacking magic and the power to return home, they assume human identities and live average human lives with the Demon King becoming an employee of a fast food joint!
[Source: Anime News Network]