Sakura Yamauchi (Minami Hamabe) and "I" (Takumi KItamura) were former high school classmates. Inspired by Sakura's words, "I" (Shun Oguri) has now become a teacher at the school they both attended. While talking to his students, he is reminded of the many days he spent with Sakura. Sakura, who was suffering from a disease of the pancreas, kept a diary of her struggle against her illness and how she tried to live with it. After he discovers the diary by chance one day, "I" and Sakura gradually start to spend more time together. Sakura is determined to live out her days brilliantly, but finally, the end draws near. Twelve years after her death, her best friend Kyoko (Karen Otomo & Keiko Kitagawa), who is soon to marry, also begins to remember the time she spent with Sakura, just as "I" does. Then, because of something that happens, the two realise what Sakura really wanted to convey over the distance of those 12 years.