In the winter of his first year of high school, Akito Hayasaka is diagnosed with a heart disease and told he has little more than a year to live. Unable to share the news with anyone except his parents, he retreats into himself, avoiding connections with those around him. While visiting the hospital for treatment, he meets Sakurai Haruna, a girl his age who has been ill since childhood and has been given roughly six months to live. Unlike Akito, Haruna speaks openly about her prognosis and claims she is not afraid of dying; in truth, she is exhausted by years of fighting her illness and longs for the end.

Akito, keeping his own condition hidden, begins spending time with Haruna. He is drawn to her candid acceptance of her fate and gradually finds himself caring about her. Haruna in turn looks forward to their meetings, and the two grow close. Wrestling with whether it is right to fall in love when he has so little time left, Akito eventually decides to make the most of the days he has. He creates a list of things he wants to do before he dies and works through it with renewed purpose.

Neither Akito nor Haruna confesses their feelings directly, each fearing that doing so would only deepen the other’s pain. Instead, they focus on helping each other fulfill unresolved wishes. Haruna’s deepest regret is a fallout with her former best friend, Ayaka Miura. Akito tracks Ayaka down and arranges a reconciliation. Ayaka, who harbors a secret crush on Akito, steps aside when she sees that the two are already in love, choosing to support their relationship rather than interfere.

As Haruna’s condition worsens, her remaining time runs out before either can speak the words they have kept inside. After her death, a grief-stricken Akito discovers a blog Haruna had been writing. In it she had recorded her true feelings, and Akito begins responding to every post, finally able to express what he could not say while she was alive. The story weaves together their quiet, fleeting days together and the separate arc of Ayaka’s unspoken love, forming a dual narrative about love with a deadline and the ways people choose to spend the time they have.