Aya Ikeuchi is a junior high school student preparing for the high school entrance exam. Surrounded by her cheerful and reliable mother, Shioka, her father, Mizuo, who runs a tofu store, and her three younger siblings, Ako, Hiroki, and Rika, she leads an ordinary but lively and happy life.

Dr. Mizuno, a neurologist at the Jounan University Hospital who examined Aya, told Aya's mother, Shioka, that her disease was thought to be spinocerebellar degeneration. This disease causes the cerebellum to atrophy for some reason and the nerve cells in the cerebellum break down, making it increasingly difficult for her to move her body.

A three-hour special of the series set five years after Aya's death and focuses on Haruto Asou, who has now become a doctor at the same hospital Aya was treated in and Ako Ikeuchi, Aya's younger sister who is a nurse in training. Haruto is caring for a 14-year-old female patient, Mizuki, who was bullied in school because of her disease, the same one that Aya had. Because of the bullying at school, Mizuki decides not to receive therapy of any sort that would make her better, because she has lost her will to live. Haruto remembers how Aya fought her illness and lived her life with her disease; therefore, he offers support to his patient.