To attend university in Tokyo, Gou and his younger sister Rihoh live at their brother's place in the city. Rihoh is the stepchild of their father's remarriage and has no blood relation to them. Rihoh harbors feelings for Gou beyond that of siblings and seizes every opportunity to tempt him with H acts, but Gou has been holding back. However, the brother who can't calm down over Rihoh's massive breasts is at his limit…
