Anastasia Mistina, known as "Mi," shares classes with Yume Kuonji and Keiko Inamura, excelling as a member of the school athletics team. Her vibrant social life revolves around close friendships, yet her overtly sexual and masochistic tendencies frequently unsettle peers. She emits provocative vocalizations resembling intimate encounters and engages in public self-stimulation, bewildering observers like Ren Uesugi during their first meeting.

Uninhibited in discussing sexuality, she finds arousal in physical pain, suggestive remarks, or misinterpreting Ren’s casual glances as deliberate advances, openly reveling in these perceived provocations. Despite such eccentricities, she navigates social dynamics adeptly, balancing sharp intellect with genuine loyalty to friends.

A distinctive business card bearing a prominent "M" hints at her masochistic identity rather than her nickname. Her defiance of conventional decorum, coupled with an unabashed curiosity for varied sexual experiences, cements her reputation as an unconventional yet integral presence within her circle.