After the mother's death, the Tenma household became a single-parent family with just father and daughter. The father worked tirelessly every day for his only child, and Yui grew up sincerely, watching his efforts. However, she harbored intense feelings for her father that went beyond a daughter's love. Unable to suppress these emotions, she resorted to masturbation daily to comfort herself. Then one night, when her father proposed remarriage, Yui's pent-up desire finally erupted—.