In this story, Shouhei Shindo’s father gets married, and now his classmate Rino Mizusawa becomes his step-sister. Shouhei is an otaku, and he’s surprised to find himself living under the same roof as Rino, who is popular and known for her GAL/gyaru style.
One day, while Rino is sleeping, Shouhei takes a sneak peek under the towel she’s using, and he finds her sleeping naked.
He can’t resist touching her soft breasts and belly, and then he becomes fascinated by her buttocks and its alluring opening. Afterward, they engage in intimate activities multiple times, and Shouhei can’t get Rino’s seductive buttocks out of his mind.