Nanase, Rio

七瀬理央（ななせりお）

She is the strict younger sister who keeps an eye on everyone else's studies.
She is entirely unfamiliar with anything sexual, making her a late bloomer in that regard.
Whenever her female siblings begin discussing anything lewd, she turns completely red.
Whenever her older brother is around in any way, she is invariably angry with him.
... Although that is the demeanor she maintains, she actually cares for her older brother deeply.
She strives to express those feelings of affection toward him, but before anyone realizes it, she strikes him with an elbow.
A typical tsundere who cannot be honest with herself.