Yuumi is the secretary of the student council. She's very pretty and is always sexually harassed by the president of the council,
Kotoko, who really likes the softness of her breasts.
She is a pretty traditional girl, very polite and has very good manners. She is considered as the second prettiest girl of the academy, right after
Aya-sensei.
She's very shy with boys, and finds it very difficult to talk with them because she suffers from androphobia.
Although she is shy and is afraid of boys and has never given her "ring" to another, she has on her arm a beautiful collection of "rings" she received as proof of confession.
She knows
Yuuki because of his "incident" with Aya-sensei.
(spoiler hidden)