理詠子～謀略の連鎖～

Yuki is a timid but friendly boy. His father passed away before and his mother is busy working as a governor of a high school. Therefore his older sister Rieko takes care of him. Rieko is so absorbed in him, keeping forbidden relationships with him but Yuki never doubts it. One day, there is a talk that their mother marries. Their new father has three children and Yuki has three new sister-in-laws. They are all confused about the situation. Rieko is the one who gets furious. She plans to insult the new sisters to trap shameless people who roll their eyes at him...