Yuuri Shibuya is an average high school student whose passion in life belong to a baseball game. His life change when an unexpected incident happened, some guys bully him and used to flush him in the toilet. His head get dunked in the toilet but surprisingly he sucked into it and ends up in another world. When he reach mysterious land, he sees some people dressed in medieval costume and speaking in some weird vernacular. There he meets Adalbert von Grantz who uses some form of magic so Yuuri understands the local language. He also meets Conrad Weller and Günter von Kleist who rescue him and take him to Blood Pledge Castle, the residence of the Maoh, where he soon finds out he is the new Maoh or Demon King will rule over “Shin Makoku” (True Demonic Kingdom). He is declared the 27th Maoh of the Mazoku (Demon Race) because of the strange power that suddenly transforms him into the Maou, deliverer of justice, this form can be recognized mainly by the longer hair and demon eyes.
The series is predominantly made up of good-looking young men which lead to an assumption of being a shōjo (anime and manga written for a female audience). The series is often mistaken for such boys love because of its calm acceptance of homosexuality in the setting such as an early plot point that ends with two male characters becoming engaged, accurately the series can be called a “male harem”. Romance is not a main theme of the series, though it has a flourishing fan-community dedicated to various romantic pairings. As the series goes it reveals that it is more about justice and friendship.