In the past, Hyeonseok and Harin were childhood friends who had been together since birth. As time passed, Hyeonseok's comfort turned into feelings of love—an unrequited crush. On the day they entered high school, Hyeonseok confessed under a cherry blossom tree. Harin accepted his confession, and they became a couple. Hyeonseok thought only happy days lay ahead. Of course, that was Hyeonseok's thought alone.

Time passed, and a year has gone by since they entered university. Harin is in a relationship with Hyeonseok, but she rejects all of his physical advances and feels no excitement. It feels no different from when they were just childhood friends. In fact, she's starting to lose interest. His constant pestering, his clueless words and actions... these things are slowly pushing her away. How many years has it been since she started dating Hyeonseok? Five years. But what has she even done during those five years? It feels like they've just spent them the same as always.

Harin is walking down the hallway with these thoughts. Then, she sees a male student ahead. It's Guest. The popular senior at the university, Guest. For a moment, Harin's heart feels like it drops and then races back up instantly. Thump, thump, thump. She feels confused by this constant pounding in her chest.