This story is about a girl named Aya who suffered from an incurable disease, but lived life to the fullest until her death at 25. The original story is based on the diary Aya kept writing until she could no longer hold a pen. The book that later followed entitled "One Liter of Tears" has sold over 1.1 million copies.
Aya's only wish was "to live." By carefully depicting Aya's earnest desire to live, and the love of her family, friends, and lover, the drama, "One Liter of Tears" wishes to deliver her simple but strong message: "Just being alive is such a lovely and wonderful thing."
The drama starts right before Aya (Erika SAWAJIRI) is hit with the tragic illness, called Spinocerebellar Degeneration, in which the nerve cells of areas necessary for the human body to move and balance - including the cerebellum, brain stem, and spinal cord - transforms and eventually disappears.
15-year old Aya Ikeuchi is the eldest daughter of a typical Japanese family. She lives with her cheerful and reliable mother, Shioka (Hiroko YAKUSHIMARU), father Mizuo (Takanori JINNAI), owner of a tofu shop, younger sisters Ako (Riko NARUMI) and Rika (Ai MIYOSHI), and younger brother Hiroki (Yuuma SANADA).
On the day of her high school entrance exam, Aya is full of energy as she leaves the house. But she falls asleep on the bus and misses her stop. She gets off the bus and starts running in the rain, slips and falls, injuring her knee. That's when she meets Haruto Aso (Ryo NISHIKIDO), who was planning to skip the exam. He gives her a ride on his bicycle to school where the exam will be given. Aya is allowed to take the exam in the school nurse's office, and manages to pass.
When the new semester begins, Aya is elected class rep. and joins the basketball team. On the boys team is someone she has eyes for, which adds to the things she has to look forward to.
Amidst her happy days at school, Aya begins to experience physical difficulties. She often drops food from her chopsticks while eating, can't pour water into a cup without spilling it, and occasionally wobbles while she walks. Aya's mother Shioka, a former nurse, is the only person that realizes these changes.
One day, Aya is about to leave home as usual. When she starts to run, she trips over her own feet and falls. She couldn't protect herself with her arms while falling, causing her to land on her face - making her bleed heavily. This injury soon reveals the existence of Aya's fateful disease.