Han Yu-an, a senior in high school, failed the SAT exams as he accidentally shifted down his answers on the answer sheet. Before him appears a handsome foreigner... no, a demon, who says he could turn back time for Han Yu-an. However, he would have to act as the stand-in for the Demon King... Can Yu-an safely return home after having this abrupt change of lifestyle? "Should I just live however I want? Because until the real Demon King returns, I'm the actual Demon King!"