In a small coastal town in Japan, a group of teenagers faces the challenges of school life and personal discoveries during a summer that promises to be unforgettable. The story follows a boy named Uminchi, who is an introspective and somewhat solitary young man. As he discovers he has a special talent for music, he immerses himself in his inner world, where the melody of the sea resonates with his deepest emotions and thoughts.
Spending time with friends, Uminchi finds himself at a crossroads when a new girl, a talented and enigmatic pianist named Maiko, enters his life. She brings a spark of creativity and energy, challenging Uminchi to come out of his shell and explore the world around them. As their friendship deepens, they begin to dream of forming a band and combining their talents to express their feelings, grappling with the pressures of family expectations and the insecurities of adolescence.
The sea, which has always been an essential backdrop in their lives, becomes a symbol of their aspirations and the inevitability of change. As the end of summer approaches and reality looms over them, Uminchi and Maiko must confront their fears and the possibility of separation, but they will also learn that music has the power to unite, even in the darkest moments. Thus, they embark on an emotional journey that marks their passage into adulthood.