Miwako Mizukoshi possesses brown eyes and waist-length brown hair. She exhibits a pronounced masochistic nature, finding arousal in public humiliation and scenarios provoking shameful attention from others, often displaying physical reactions like salivation in anticipation. This drive extends to behaviors such as consuming insects to elicit disgusted reactions, which induces delight in her. She actively seeks situations involving public observation during sex and consistently volunteers for experiments related to abnormal sexuality, showing specific interest in group sex and being filmed during intercourse.

She initially enters a relationship with fellow seminar attendee Komugi Musashi, readily accommodating his sexual preferences. Their dynamic involves mutual exploration of their respective fetishes, with Miwako providing an outlet for Komugi's inclinations. However, the relationship ends as the novelty fades for Miwako. She subsequently forms a connection with Yuuji Horii, discovering he offers a more intense level of the thrilling sensation she craves, fulfilling her need for heightened stimulation more effectively than Komugi.

Within the Abnormal Physiology Seminar, Miwako demonstrates notable enthusiasm for participating in experiments and discussions on abnormal sexuality. She frequently volunteers as a test subject, driven by the potential for public scrutiny or humiliation. Her engagement in the seminar's academic pursuits, particularly those investigating abnormal body functions and human physiology as a living laboratory, is marked by this active participation, earning her recognition as the star pupil.

Her character progression centers on her pursuit of experiences that satisfy her masochistic needs. The transition from Komugi Musashi to Yuuji Horii illustrates development driven by her search for increasingly potent stimulation. Her consistent engagement within the seminar remains defined by her readiness to serve as a subject for investigations into abnormal sexuality and physiology, seeking situations aligned with her psychological inclinations.