Hikaru's younger sister crosses the line between parents and children when she is alone with her father-in-law. One day, when my sister Haruka comes home, I see her father-in-law having sex ... When Haruka tells his father-in-law about it, his father-in-law is far closer to closing his mouth and eventually has a relationship. A strange love triangle between a beautiful sister and her father-in-law was about to begin ...