Oki Natsume

Fetish: Infantalism
Weak spot: bodily secretions (Saliva, sweat, semen)

The protagonist's homeroom teacher and the school's sister. Kotori's older sister whose appearance gives out a strict and serious impression. She treats all of the students equally regardless of their sex; if they're a good student, she won't oppose their enrollment.

Natsume has always been serious since she was little and cannot understand why her sister is turning into a delinquent student, and it hurts her.

Being so serious for so long Natsume has trouble to expressing her feelings. She also wants to be spoiled and do whatever she wants, just like her sister.