Sister, known alternately as Onee-chan or Teacher, is the titular character’s older sibling and a homeroom teacher at their school, where she also advises the Magic Club. With brown hair, green eyes, and a perpetually warm smile, she dresses in casual professional attire—a pink shirt layered under a purple sweater, tan pants, and red flats. Her affectionate but mischievous nature manifests in playful teasing of her younger sister, whom she addresses as “precious” or “Little Sis,” often provoking irritation. This dynamic includes coaxing her sister into wearing costumes for performances, blending humor with encouragement.

Married to the composed, sharply dressed Mimura, their relationship surfaces in an episode where he seeks advice to choose her birthday gift, inadvertently sparking misunderstandings among peers. The incident underscores her marital bond and family-centered values. As a teacher, she approaches responsibilities with levity, yet intervenes decisively in club affairs when needed. Observant of her students’ dynamics, she subtly capitalizes on the protagonist’s crush on her sister for lighthearted amusement.

While her history beyond teaching and family ties remains uncharted, her influence weaves through both comedic interactions and pivotal growth moments, particularly aiding her sister’s journey to conquer stage anxiety. Her portrayal remains steady across media, anchored in consistency rather than narrative expansion.