Mitsuki appears to be a reserved and calm 15 year old girl who recently moved in Yuuya's house after their divorced parents got married again. She encountered and was possessed by an angel one day on her way home from school shortly after transferring, whom the angel holds affection for Mitsuki's older brother. As a result, she often alters between her normal self and the angel's personality around people, especially to get Yuuya's attention.

A Chastity belt had been tied onto her with a magical love gauge measuring Kotobuki Hiyori's content on her love and sexual life. The gauge fills up every time Kotobuki Hiyori is satisfied (e.g. after having sex with Mitsuki), but goes down slowly over time when Kotobuki Hiyori's love life is neglected. The belt also brings inconvenience to Mitsuki Kanzaki, especially during urinating. The belt can be released for 3 minutes for relieving purposes but locks itself back after the 3 minutes and can only be opened again after an hour.