It was the spring of 1956, roughly 10 years after the end of the Pacific War.
A new teacher named Rieko Sakamoto is assigned to an elementary school in Kiba, downtown Tokyo. At the same time, Shizu Miyanaga, a transfer student from Kobe, joins the class #4 of the 6th grade. Shizu is a bright, pretty girl who dreams to become a singer. Blessed with both athletic and academic abilities, Shizu quickly becomes the center of everyone's attention in the class. Akira, the son of a joiner and also the class president, starts to develop a special feeling for Shizu.
Led by Ms. Sakamoto, the school tries to compete in the local chorus competition that takes place at the end of the year. From class #4 of the 6th grade, Ms. Sakamoto chose Shizu along with her friends Kimiyo, Hikaru, Yayoi, Akira, and smart Sugiura, who is the son of a doctor, as choir singers. Ms. Sakamoto has a strong passion for music education, because her older brother who died in a Kamikaze mission wrote the will that she should become a school teacher and pass down Doyo to the children. The students who were not selected for the choir are excited about the competition, too, including the bossy Gon who somehow looks lonesome and Akira's friends Yoshio and Teru. One day Akira, Gon and their friends commit an act of delinquency. As a result, the school is forced to withdraw from the chorus competition at the discretion of teachers. While the friendship between Akira and Shizu remains impaired due to this incident, their summer break started.
During the break, Shizu accidentally drowns in the sea. Her death struck Akira hard, but with Gon's strong suggestion who had a secret affection for Shizu, Akira decides to plead with the school to let the students compete in the chorus competition. Moved by Akira's enthusiasm, the school principal gives the students a permission to join the competition. The students start the hard singing practice for the competition in winter, holding deep thoughts not only for Shizu but also for Gon who suddenly transferred to a different school.