Every day, a young girl dressed in a mask stands by the shore and sings a melancholy tune. Nino Arisugawa has been singing her songs to the water since she was a youngster, tied by a pledge she made with her two childhood friends—her first love, Momo Sakaki, and a guy who wrote music, Kanade "Yuzu" Yuzuriha. Despite having never met, the boys both agreed that if Nino was ever torn from them, her voice would be the beacon that would reunite them. After six hard years, Nino, Momo, and Yuzu have finally been assigned to the same high school. However, the passage of time has altered many aspects of their lives—even as Nino continues to strive to accomplish his dreams.