Shiina Yuki

She is the principal of Tenya Academy. She is Riko's biological mother.

Her husband, who is a year older than her, was the head of the school, but he disappeared this summer after transferring the rights to the school to an unknown company. She is suspicious of her husband's disappearance and does not trust the main character who has been assigned to her as the school's director.

In order to find out who is behind her husband's disappearance, she asks Aoi Sakazaki, a janitor, to investigate.