Mizunuma is a young woman of average height and long brown hair.
She is usually very kind, and seems to be popular with her students.
She is Osamu's homeroom teacher, and introduces the class to Yūma. She later informs him that rings were not allowed. When the Mole Mods attacked the school, she had her class evacuate according to procedure.
When the Trion Warriors begin pouring in, Osamu orders her to evacuate the students, to which she complies.
- "Mizunuma" (水沼?) literally translates to "water swamp".
- Her Japanese voice actress, Umeka Shōji, also voices Yuu Kunichika, Itsuki Fujisawa and Yūko Kumagai.
- Compared to her original design, Ashihara made sure that he made her cuter.