Haruki is a high school student who has no friends. The boy comes across a small notebook one day. Sakura, a fellow classmate, is the proprietor of the diary. Sakura informs Haruki that she has a terminal disease, but he shows no empathy for her. Sakura gets fascinated by the boy’s behavior and follows him around.

Despite Sakura’s efforts to become friends with Haruki, he shows little interest in her. Sakura, on the other hand, is persistent and “forces” Haruki to hang out with her. After spending more time together, the two became closer.

Everyone in the class is talking about Sakura and Haruki. At school, there are dating speculations circulating about those two. Nonetheless, Kyoko (Sakura’s best friend) is not happy. Despite being Sakura’s closest friend, Kyoko is unaware that her best friend is dying from a terminal illness.

Sakura’s health weakens after they go on a trip together. Haruki pays a visit to Sakura in the hospital. Sakura gets out of the hospital one day and accompanies Haruki to view the fireworks. Sakura is later discharged from the hospital.

Sakura and Haruki plan to meet together to celebrate her return. The boy chooses the first coffee shop they visit together. Sakura, on the other hand, does not appear. Haruki returns home to hear that Sakura has died. Sakura was on her way to meet Haruki when she was stabbed in the chest by an unknown person. This news totally devastates the youngster, and he misses her funeral.

Haruki travels to Sakura’s house after fully accepting her death. The boy meets Sakura’s mother there. Haruki receives her daughter’s diary from the mother. Haruki imagines a final meeting with Sakura while reading her final notes to him. Haruki meets Kyoko after making peace with Sakura’s death. He shows Sakura’s diary to her. Kyoko storms out of the coffee shop, furious. Haruki has enraged her by not telling her the truth.

Haruki chases Kyoko. Despite Kyoko’s harsh attitude, Haruki thinks that they can become friends one day (as Sakura wishes). Haruki and Kyoko travel to Sakura’s cemetery as friends a year later.