The film begins when Mayu and Takuma were children. They were friends since they were 8 years old. Takuma has a heart disease and he is treated by a cardiologist who happens to be Mayu's father. One day, Takuma and Mayu overhear that Takuma will not live past the age of 20 due to his condition. However, their friendship grows and Takuma becomes Mayu's first love. When they are out playing in the fields, Takuma promises to marry Mayu when they turn 20.