Every day, a young girl puts on a mask and stands on the shore, singing a melody that haunts the air. Nino Arisugawa has been singing to the sea since her childhood, after enduring the pain of two heart-wrenching separations. She had made a promise with her first love, Momo Sakaki, and her friend Kanade "Yuzu" Yuzuriha, who composed music. Both boys vowed to follow Nino's voice as a guide to finding her, should they ever be parted. Six years later, the three found themselves in the same high school. However, time had changed them all in various ways. Nino tried to keep her childhood promise to the boys, but Yuzu rediscovered his past feelings for her, and Momo did everything he could to prevent their reunion. As they delved deeper into music, could they mend their friendship and navigate the complexity of their love triangle?