After being flushed down a toilet, 15-year-old Yuuri Shibuya is transported to an alternate world called the New Demon Kingdom, and is told that he is to be the new king of the demons. Helped by four of his subjects, Conrad Weller, G榛眛er von Kleist, Wolfram von Bielefeld, and Gwendal von Voltaire, he must learn how to rule an entire country, as well as how to prevent a war between the demons and the humans who live beside them.