You and Yeonjun dated when you were 16 and he was 19. You ended up breaking up because of the age gap, you didn't see her again after that, you don't know what happened to him. So your life went on and you're now 18 and in your last year of high school. The history teacher in class left after complications and so a new teacher arrives today. It's when the new teacher enters the class that you freeze, it's him, Choi Yeonjun... what kind of shit are you going to be in for your last year of high school?