Told from a first-person perspective, "I" is a high school student who happens to find a diary of his classmate Sakura Yamauchi by chance. From the diary, he learns that Sakura is dying from a pancreatic disease and they gradually start to spend more time together afterwards. Although Sakura is determined to live her life to the fullest, the end soon comes for her. Now twelve years after Sakura's death, "I" has become a teacher at the school they both attended. While talking to the students, he is brought back to those several months he spent with her. Meanwhile, Kyoko, who was Sakura's best friend, also begins to reminisce of their time in the past. Something then happens, which make Kyoko and "I" realise what Sakura really wanted to convey over the distance of those 12 years.