Satou Yoshimi

Yoshimi is a second year student from class 2-C, Leo's classmate and a member of the student council. She is popular with everyone, she is an honour student, is quick in her movements, is a good cook, and is sweet-tempered. She puts the brakes on Erika once in a while, for Erika tends to go her own way without consulting anyone. She at first appears to be a very mature person, however, her true nature is quite the opposite. Erika is her close friend who understands her true self. She often approaches Leo, who does not notice Yoshimi's deep feelings for him.

Spoiler

Her Yandere personality is born from family situation. father cheated on wife. Her mother became angry/crazy taking out her problems on Satou. Her mother became Yandere, hating her husband for cheating/lying but kept up public appearance. Satou discovered masturbation as one of her outlets at time becoming a nympho as only way to comfort self, eventual turning into her mothers personality as Yandere.