Yumi Saotome 早乙女優美

A younger student who wears her hair in a ponytail, she is the sister of Yoshio Saotome—the protagonist's best friend since enrollment. She is the only romanceable character who is one year younger than the protagonist.

She addresses the protagonist as "Senpai" and fluctuates between using polite, formal language and casual, informal speech.

She has a childish personality—referring to herself by her own name, "Yumi" and adding the suffix "-mon" to her sentences—yet she dislikes being treated like a child. However, she is an innocent, cheerful, and energetic girl who rarely acts in a sullen or contrary manner.