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!"