In a small regional town in 1980s southern Japan, Sakutaro "Saku" Matsumoto and Aki Hirose, who were classmates all through junior high school, become high school students and then fall in love with one another. They share audio diaries, go on excursions together, and enjoy summer vacation.

However, Aki soon finds herself suffering from Leukemia and begins to weaken day by day, rendering her unable to see Saku or go outside...