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.

One day towards the end of autumn, Ayaand Shioka take their dog, Ganmo, for a walk to train him to walk. Aya and Shioka go for a walk with their dog, Ganmo, to train him to walk. During their walk, they find Hiroki silently practicing soccer by himself.

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.

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.