Daeun is moving to Seoul with her older sisters. In the elevator, she crushes with the man who lives upstairs at first sight. She entered the school with flutter and she found man who lives upstairs, in the same class. Did love like destiny come to Daeun?

Daeun does not give in to the wall of Seunghyu's mind and expresses her mind without hesitation. At some point, Seunghyu began to take an interest in Daeun…

The two who have a subtle atmosphere after their first date. Realizing his pounding heart, Seunghyu ask Daeun out.

Seunghyu and her relationship that seemed to be happy. However, Hong yeon, who claims to be Seunghyu's girlfriend, suddenly appears and cracks between the two begin.

Seunghyu, who was trapped in a world alone, distancing himself from people. As Seunghyu's past is revealed on the surface, Daeun's anxiety is growing…

The memories of the past that Daeun wanted to forget make her suffer. By the side of Daeun, who has lost her will to live, Seunghyu and Yoo Il find a way to rescue her from despair.

Seunghyu visited Hojun, and Eunha visited Daeun. Will Seunghyu and Daeun be able to overcome the growing pain and become happy again?

'Nineteen' that heal their pain in their own way. The memories of the days that were incomplete but warmer than anyone else.