"It was the happiest day in the world." Our sad and fleeting "love with a deadline" has begun.

In the winter of his freshman year of high school, Akito Hayasaka is diagnosed with a heart disease and told that he has little time left to live. In the midst of despair, Akito meets Sakurai Haruna, who is hospitalized at the hospital. Haruna, too, is seriously ill and has only a few days left to live. Akito begins to talk with her, hiding his illness, and becomes interested in Haruna, who says she is not afraid of dying. Can I still be in love with her?　 The days that pass by as he asks himself these questions begin to change?

The story is the ultimate story of pure love, with a sense of fragile beauty and tenderness in their daily lives, which are depicted in a lighthearted manner.