There's is a boy named Yang Yoseob, Lee JiEun or also might be called IU was his girlfriend 3 years ago..... but, they broke up because Jieun left Yoseob because she said she had an another boy she like. Because what happened, Yoseob was really hurt. Yoseob really loved her a lot, but  the whole time Jieun didn't have real feelings for Yoseob. It was Yoseob's first time being hurt a lot. But, when this girl Jiyeon comes into their lives..........