Following an injury that prevents him from further pursuing baseball, Yuuhei Kishimoto, a normal high school student, now has too much time on his hands. On the upside, this allows him to finally pay proper attention to his pet—Satan. Despite his seemingly difficult personality and the fact that he is, well, the devil king, Satan doesn't bite. In fact, he is a caring, shy, and quite easy to understand pet. Yuuhei, therefore, takes care of his pet as he would any other—he feeds Satan, takes him out for walks, and showers him with affection. As a bonus, Yuuhei sometimes has to keep Satan from going berserk or summoning creatures from the underworld, as well as maintain Satan's status as the devil king.

Full of light-hearted charm and humor, Uchi no Maou Kamimasen yo follows this unusual owner and pet duo through their daily lives filled with both ordinary and supernatural events.