Every day, a young girl in a mask serenades the sea with a haunting tune. Nino Arisugawa, scarred by two crushing separations in her youth, shares her melodies as a pledge to her childhood companions—her first crush Momo Sakaki and the musical prodigy Kanade 'Yuzu' Yuzuriha. Unbeknownst to each other, both boys vowed that Nino's voice would guide them back if they ever drifted apart. Now, after six years, fate reunites Nino, Momo, and Yuzu at the same school. Yet, time has reshaped their relationships—Nino strives to honor her childhood pact, while Yuzu's old affections resurface, and Momo fights to keep them apart. As music intertwines their fates, can they reconcile their past, navigate the complexities of their triangle, and find harmony amidst love's discord?