Park Hyebin is 16 this year, her parents are dead in an accident when she was at the age of 15. Now Park Chanyeol, her oldest brother, takes care of her and her second brother, Jongin.

Zelo, aka Choi Junhong, is 16 this year and his parents are working overseas, leaving his twin sister, Choi Tara, to take care of each other.

Park Chanyeol,18, is the most popular student in the university and he is dating Tara. He gets to know who Hyebin sits beside for the rest of the year and coincidentally, Hyebin sits beside Zelo. 

Park Hyebin is a friendly and cheerful teenage girl, although she does not talk to strangers she don't know, Zelo gives her a sense of security that made her start the conversation. Zelo is also a cheerful and friendly teenage but when it comes to love, he has difficult issues. When Hyebin talked to him, he decides to confess to her that he likes Hyebin, and it was a love at first sight.

However, Zelo was told to go to a pub together with his friends. He could not hold is liqour well and eventually got drunk. The next morning, Hyebin went into his house with the spare keys Zelo gave her and saw Zelo sleeping with another girl. She didn't listen to the whole story Zelo told her, ran away and got into a car accident which made her lost her memories of the age 15 and 16, including Zelo.

3 months later, Hyebin finally wakes up after a long sleep. But she could no longer remember Zelo. Along the time, she received some fragrants of memories but still couldn't picture them together. Then slowly, from her addresses from Zelo, from Mr Choi, Zelo,then to oppa, she realised she fell in love with Zelo again.

But when Zelo brought her to his house, they went to the bedroom and a lot more memories went back regarding the incident where Zelo slept with someone else and every part of her memories rushed back and fainted.