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.

Aya is told by Dr. Mizuno, a neurologist at Jounan University Hospital, that she has spinocerebellar degeneration. Returning home with her mother, Shioka, Aya tries to force a smile and act brave, but she is unable to accept her illness and begins to cry.

Aya continues her rehabilitation under the guidance of rehabilitation specialist Tanabe. However, Aya's behavior is different from usual, and she is unable to put any effort into her rehabilitation, and finally sits down as if she has given up everything. Mizuno, the doctor in charge of Aya, is concerned about his condition.

A new year has dawned. Aya, who now has even more difficulty walking than before, uses a wheelchair, but with the support of her family, including Shioka and Mizuo, she lives her days cheerfully and cheerfully.

Aya goes to cheer on the basketball team's rookie tournament and congratulates Mari and Saki for making it through to the first round. Then, Shioka and her friends come out of the school building, having just finished the parents' meeting. Aya notices Shioka's gloomy expression and for some reason feels uneasy.

Aya has been sent to live as a boarder at a school for the disabled. One of the biggest helps to her is an electric wheelchair. She is determined to walk where she can by herself, but being able to move freely on her own is a great joy for her.

Aya has a progressive dysarthria that makes it difficult for her to pronounce words smoothly. Mizuno, the doctor in charge of Aya, tells Shioka and Mizuo that it will be difficult for Aya to go on to higher education or find a job after graduation from the school for the disabled, and advises them to work on her rehabilitation at home.

Aya, now 20 years old, has been writing a diary while staying in a hospital attached to Jounan University Hospital. At the same time, Aya continued to contribute to the newsletter of the "Fureai no Kai," a group she started at the request of Kiichi, a volunteer who took care of her when she was at school for the handicapped.