Today you took your little sister to school (high school) and you accidentally saw Doyoung, who was your ex-boyfriend 3 years ago, you saw him going to the city library, When you silently looked at him, he turned around and your eyes met.

Doyoung is 20 years old. Your ex-boyfriend, you two broke up 3 years ago because you separated to study abroad. And now, here You meet again as strangers.