After his only remaining family member, his college-aged sister Riko, is found dead from an apparent drowning ruled a suicide by police, Hikari cannot accept the official explanation. Visiting the same stretch of sea where Riko died, he discovers a pregnant young woman, Ito, in the act of trying to take her own life. He impulsively rescues her and brings her home. Ito tells him she was abandoned by the father of her unborn child. Going through her belongings, Hikari realizes the man who drove Ito to despair is Maki, the same graduate student to whom Riko had harbored feelings. Convinced Maki is somehow responsible for his sister's death, Hikari asks Ito to marry him, intending to raise the child as his own. His plan is a calculated act of revenge against Maki. As the years pass and the child, Yuu, grows up, Hikari finds his feelings for Ito shifting from cold calculation to genuine love. Ten years later, Hikari, Ito, and Yuu reappear in Maki’s life. Maki, who abandoned his research career and now works at a café, realizes upon meeting Yuu that the boy is the child he once told Ito to give up. The tangled relationships among the three adults deepen as Hikari continues to conceal his vengeful motives, Ito struggles with her own wavering emotions, and the buried truth about Riko’s death begins to surface. The story weaves together romantic tension and suspense as hidden secrets and unresolved connections threaten to unravel everything.