Jung Yu Jin is an outgoing, cheerful and popular 18-year-old girl at a high school in Chuan Chun. Her father Jung Xin Zhou has passed away, and she and her younger sister is raised with their mother.

Yu Jin's family is close to Kim Sang Hyuk's family, and Yu Jin and Sang Hyuk grew up together. Sang Hyuk is an obedient student who is well-liked by classmates. He has been admiring Yu Jin all along.

One day, Yu Jin and Sang Hyuk were late for school. Yu Jin managed to squeeze into the bus by herself, and fell asleep on the bus on the shoulder of Kang Joon Sang. Joon Sang is a quiet, talented student who has transferred to the school in Chuan Chun where Yu Jin studies, and he is there to look for his father.

Joon Sang identified Kim Zhen Yu, a Mathematics Professor, as the person he is looking for. Zhen Yu is Sang Hyuk’s father. Joon Sang is hostile towards Sang Hyuk, and tried to compete with Sang Hyuk in every way...

Wu Choi Lim, who is in the same class as Yu Jin, is interested in Joon Sang. She made an open declaration that Joon Sang belonged to her.

Joon Sang slipped into the University to attended Zhen Yu’s Mathematics lecture. The latter was duly impressed with Joon Sang's talent. Zhen Yu invited Joon Sang to go to his office to discuss mathematical problems with him after school regularly.

At home, Joon Sang's mother, Kang Mei Xi (who was a pianist), asked why him wanted to be transferred to that school, and brought up the topic of Joon Sang's father. Mei Xi told Joon Sang that his father was dead, and he should go to US with her after her concerts ended.

Yu Jin and Joon Sang were late for school again. In order to avoid the fierce teacher who was guarding the front door, Yu Jin suggested that they could help each other to sneak into the school, via climbing over the wall. Joon Sang helped her up the wall and jumped over from the other side by himself easily. Yu Jin, who was left sitting on the wall, panicked and begged Joon Sang to help her down...

Joon Sang was supposed to co-host the lunchtime broadcast session with Yu Jin. Instead, he was relaxing at the rooftop, under the sun. Yu Jin was not happy and broadcasted to the whole school that she had an irresponsible partner... When Joon Sang went to the broadcast room, through the half-opened door, he caught the sight of Yu Jin dancing to the music of Abba, and was fascinated.

In the music room, the music teacher was testing each student's piano skill. Joon Sang sat at the piano, not playing. Yu Jin explained to the teacher that Joon Sang was a newly transferred student (whom might not know the test).

In the evening, Yu Jin went to the market to see her mother who sells clothing there. On the way home, she was molested by a drunk. Joon Sang passed by, got into a fight when tried to rescue her. Both of them were taken to the police station. There, Joon Sang realised that Yu Jin's father, Xin Zhou, is already dead. When she asked about his father, Joon Sang replied that he did not have one too.

The next day, both were teased by fellow classmates as they were with band-aids. In order to thank him, Yu Jin volunteered to teach Joon Sang how to play the piano, without realising that Joon Sang can actually play very well. At the music room, Joon Sang played a piece of music titled "the first time". While Yu Jin was fiddling with the piano key, Joon Sang saw from the window that Sang Hyuk was looking around for Yu Jin. Joon Sang decided to take Yu Jin out of the school. They took a bus to the lake and spent the afternoon there. In the evening, when Yu Jin returned home with Joon Sang, she found Sang Hyuk with her school bag, standing in front of her house.