Rio Nanase  

, 七瀬 理央 （ななせ りお）

She is the stern little sister who watches after the studies of the others. Completely unaccustomed to anything related to sex, she’s a late bloomer in that subject matter. Whenever her female siblings start to talk about anything lewd, she totally gets red in the face. Whenever her older brother is in front of her somehow or another she’s always angry at him. ... Though that is the attitude she takes, she actually really likes her older brother. She tries her best to show those feelings of love towards him, but before anyone knows it, she hits him with an elbow. A typical tsundere who can't be honest with herself.