With only a year left to live, 17-year-old Akito finds new meaning in life by bringing joy to a terminally ill girl who has just six months remaining.

Toru Kamiya performs a false confession of love to stop his classmates' bullying. The story begins when Maori Hino, a girl in his class (whom Toru has made the false confession to) gives him three strange conditions for going out with him: "Not to talk to her until after school", "To keep communication brief", and "Not to fall in love with each other". Gradually, the promise of "Not to fall in love" falls apart, and Toru finally cannot hold back his feelings and confesses his love to Maori. However, Maori confesses to him that she has anterograde amnesia, which causes her to lose her memory in a day. Her memories and experiences are reset every day, and she writes down the day's events in a diary and wakes up early in the morning to review them in order to keep her memory alive. Toru is devoted to bringing her as many happy days as possible.