The protagonist, Sakamoto Taichi, begins his new life as a university student in a new city, having left his hometown and his girlfriend, Chika, behind. The narrative picks up three days after his arrival, with Taichi settling into his one-room apartment. He reflects on his difficult decision to leave, driven by Chika's infidelity. He had kept his true university choice, a national university, a secret from everyone, including Chika and his friends, to achieve his goal of escaping his past and pursuing his dreams. His departure was akin to "running away," marked by breaking up with Chika via a letter to avoid confrontation.
Taichi attempts to cook for himself for the first time, making curry. This mundane task triggers memories of a middle school camp where he and Chika, then not yet dating, worked together. He recalls Chika's bossy but ultimately caring nature during that time, and a moment where she cried after he thanked her for her guidance. This sentimental recollection is interrupted by a call from his older sister, who informs him that Chika visited their home. His sister reveals she told Chika that Taichi had already moved out and was living alone, and then firmly told Chika to stop contacting Taichi and their family, effectively ending any further contact. Taichi apologizes to his sister for the trouble, and she encourages him to forget the past and focus on university.
The story then flashes back to two days before Taichi's departure, when he decided to write a letter to Chika. He chose a letter to ensure she would receive it after he had already left, preventing any immediate reaction. He struggles with writing a formal letter, researching etiquette online. He decides to include his decision to attend a different university, an apology for breaking his promise, the reasons for their breakup, gratitude for their memories, and well wishes for her future. While writing, he recalls confessing to Chika in middle school and their subsequent five-year relationship, including their promise to attend the same university. He also remembers the pain of discovering Chika's affair, which fueled his determination to excel academically and move away.
The narrative shifts to Chika's perspective. She is a student who secured admission to a private university via early recommendation. She has been living a relaxed life since her acceptance, often staying up late and socializing. She acknowledges her infidelity with a person named Satoshi, but considers Taichi her primary partner and believes he kept his promise to get into the same university. She notes that Taichi has been distant lately, but assumes he is busy with family matters and that they will reconnect after spring break.
Chika receives a letter from Taichi. Upon reading it, she is shocked to learn he was accepted into a national university and that he is breaking up with her. Her attempts to contact him via phone are met with an "unavailable" message, and she realizes he has changed his phone number. Panicked, she rushes to Taichi's home, where his sister, Eriko, answers the door. Eriko confirms Taichi has moved out and reveals that the family has known about Chika's infidelity for a while, and that Taichi broke up with her because of it. Eriko firmly tells Chika to leave them alone. Devastated and realizing the extent of her actions, Chika reflects on her past behavior, her neglect of Taichi, and her regret over her affair. She tries to find Taichi's new whereabouts through mutual friends but is unsuccessful.
The story returns to Taichi on his university's entrance ceremony day. He walks to the university, reflecting on the pleasant climate and the blooming cherry blossoms, which evoke a sense of nostalgia and a bittersweet reminder of his past with Chika. He arrives at the university, feeling overwhelmed by the crowd of new students. During the ceremony, he reminisces about the conversation with his sister where he decided to aim for a national university as a form of revenge against Chika for her infidelity. He recalls his father's encouragement to work hard and prove himself.
After the ceremony, Taichi meets Mizunami Iroha, another first-year student from Fukui. They bond over their shared rural backgrounds and their dreams of becoming teachers. Taichi, feeling overwhelmed by the circle recruitment activities outside the auditorium, offers to escort Iroha to the main gate. During their walk, they accidentally hold hands, leading to an awkward moment for Chika. Taichi, relieved that he hasn't been perceived as a harasser, parts ways with Iroha, taking photos of himself with the cherry blossoms to send to his mother. He feels a pang of loneliness, realizing that this should have been a moment shared with Chika.
Chika, still unable to contact Taichi, attends the university entrance ceremony alone, feeling out of place and resentful of others' happiness. She reflects on her past relationship with Taichi, their promises, and her regret over her actions. She recalls how Taichi worked hard to get into the same high school as her, and how she later pressured him to attend the same university, while she herself was not as dedicated. She realizes she had been neglecting Taichi and her own feelings.
Taichi finds himself struggling with university registration. He reconnects with Mizunami Iroha at the student affairs office, and she helps him navigate the process. They discover they have many classes in common and decide to explore course options and seminars together. Taichi finds himself enjoying Iroha's company, which reminds him of his early days with Chika, but he acknowledges that Iroha is different and appreciates her supportive nature. He feels a sense of renewed hope and enjoyment in his new life.
Chika, still consumed by regret, reflects on her past interactions with Taichi, including his avoidance of her and his past rejections of her advances. She realizes she had been selfish and unappreciative of his efforts. She longs to apologize to Taichi but is unable to reach him. She spends her time looking at photos of him, feeling a deep sense of loss and regret.
Taichi continues to spend time with Iroha, finding her helpful and enjoyable company. He reflects on how Chika's actions, while hurtful, ultimately pushed him to pursue his dreams. He acknowledges that his current path is a result of their shared history, even if it ended negatively. He finds himself relying on Iroha for academic guidance and enjoys their growing friendship.
