At her husband's suggestion, Haruki Sato begins private swimming lessons taught by Nana Aida. Haruki, whose feelings for her husband have faded, secretly harbors romantic emotions for Nana—and during one lesson, she suddenly kisses her, stirring Nana's heart. Lonely and emotionally vulnerable, Nana is deeply moved by Haruki's warmth, and gradually their bond intensifies. As passionate love ignites between them, new changes begin to unfold within both of their families. A compelling portrayal of adult emotions, where tenderness and desire intertwine.