Yuri Kashiwaga was once known as a genius pianist. One day, she returns to her hometown in Goto Islands from Tokyo. There, she begins to work as a temporary teacher at a middle school and advisor for the school chorus. The chorus aims to take part at a competition. Yuri gives the members of the chorus members an assignment. She instructs them to write a letter with the title of “To myself 15 years later.” The 15-year-old boys and girls write about their secrets and worries.

As a child, Ono Tsubasa saw a Shirato baseball game on TV and was amazed at the Trumpet player in the band playing. Now, in order to play the Trumpet, she enters Shirato High School. There, she meets Yamada Daisuke, a catcher for the baseball team. With each others support, they go towards their dream of playing at Koushien.

Takatoshi Minamiyama (Sota Fukushi) majors in art at an university in Kyoto. On the train to the school, he sees Emi Fukuju (Nana Komatsu) and falls in love with her at first sight. Gathering up all his courage, he speaks to her. They begin to date and enjoy happy days together, but Emi reveals her secret to him.

Hibiki Shimada, a normal 17-year-old high school student, still does not know how to fall in love—although surrounded by love “experts”—until one day she realizes that she’s fallen in love with her hot and nice 26-year-old teacher, Itou. She then takes a path to make her teacher understand how she feels for him.

Teenager Kazuki Miyaichi has always felt unloved by her mother due the circumstances surrounding her birth. Because she harbors anxiety and perceives herself as being worthless to others, she engages in acts of juvenile delinquency. One day, a transfer student from Yokohama named Eri introduces her to Hiroshi Haruyama, a reckless youth who’s a member of the “Nights” motorcycle gang. Kazuki finds herself increasingly drawn to Hiroshi over time, but he soon becomes leader of the Nights and gets caught up in a conflict with a rival gang.

When she was a middle school student, Futaba Yoshioka liked Kou Tanaka who was unlike the other boys and quite gentle. Kou Tanaka then moved away and they lost contact. At the end of Futaba Yoshioka’s first year as a high school student she meets Kou Tanaka again. Kou Tanaka’s name has changed to Kou Mabuchi and his personality seems different from his middle school days.