After saving him from drowning, Kou harbors unrequited feelings for his classmate Ayame, whom he affectionately labels a mermaid. Ayame, however, pines for Kou's older brother, the swimming club's advisor. Despite Kou's willingness to sacrifice everything for her, Ayame remains fixated on his brother’s love. As Kou watches Ayame yearn for unattainable affection, he questions her choices. Can Kou, indebted for Ayame's past rescue, someday repay her with a gesture of his own?