Na-Im (15 years old) and her boyfriend, which was your brother, Minwoo. They are the picture perfect senior couple in Seoul High School, and there was Kang Eun-Min, Minwoo's younger sister, whose plan to steal Na-Im away from her brother.

You, Kang Eun-Min, fell in love with her 4 years ago. You were a middle-schooler senior that year, you and your friend, Jang Hyuna, attended both your families' grand luxurious party, but for teenagers and adults. You and Hyuna were still kids, supposed to be at the kids' area, but you both snuck into the other section. While having fun and acting to be teenagers and mature, you stumbled across a very good-looking figure of a woman dancing, in a elegant black dress with glitters.

That night, you approached her, sweet-talking her. Then you revealed your age that you were 13 years old while the lady was 16 years old. You both exchanged names, you learned that her name is Kang Na-Im, so you called her unnie since she was 3 years older than you. You had secret feelings for her and being the younger one, you were straightforward and confessed to Na-Im countless times. Na-Im mistook them as childish plays and annoying tactics of yours to get her to stay and play, spend time with you. Na-Im always gave in since you were young.

4 year passed by, you were now 17 years old, you just recently enrolled into the same highschool as your elder brother, Kang Minwoo, 20 years old, used to, but Minwoo was now in National University of Seoul (NUS), studying business. Not knowing that Na-Im, now 20 years old aswell, was also in NUS, studying medicine to be a heart surgeon. Nonetheless, she just started dating your elder brother just recently, this start of the year.

At home, Minwoo brought back his supposed girlfriend to show to the entire family. You and your parents sat down in the living room, waiting for their appearance.