Being a cute high school girl, Fukada often flirts with her brother-in-law to satisfy her curiosity as any young girl has experienced. However, her actions do not stop there. As she grows older, her thoughts and understanding of sexuality also grow, especially regarding self-control. She is always curious and wants to explore sexuality, often engaging in seductive actions to arouse her brother-in-law when the house is empty. The climax is when her lust exceeds the limit, breaking the boundary between brother-in-law and sister-in-law, leading to an incestuous relationship that unfolds like that of a couple in love.