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.

With the choir competition just 10 days away, Aya, Haruto, and the other members of Class A of the first year are eager to practice. However, Aya, who has begun to notice something wrong with her body, sees blurred music during chorus practice and is struck by an inexplicable anxiety.