Naka-Goto Junior High School is situated on an isolated island in Nagasaki Prefecture. Yuri Kashiwagi returns to her hometown for the first time in many years as a substitute for music teacher Mrs. Matsuyama who is taking maternity leave. The students are enthusiastic when they hear the beautiful Miss Kashiwagi was a renowned pianist in Tokyo. However, she has no intention of playing the piano for them. When Miss Kashiwagi grudgingly takes on the role of advisor to the choir, she assigns the students homework. ‘Write a letter to yourself 15 years in the future,’ in the hope that it will give them a deeper understanding of the set song, [Tegami - Haikei 15 No Kimi He - ].