Yuuki Saori

Saori is a second grade high school student. She becomes Keita and his sisters' step sister from his father's remarriage. Ladylike and beautiful she's also perfect in housework and cooking. Because she was an only child, she feels happy for having Keita as a "little brother" and she also becomes closer with her new little sisters. She becomes a good elder sister for Erina.

Spoiler

However that was the outside appearance. Her true character is she likes to tease others without mercy, becomes extremely excited, and unexpectedly perverted. She aims for Keita's chastity.