Rui Sukiyabashi, a mathematics teacher at the protagonist’s school, stands 1.65 meters tall with a poised demeanor accentuated by her violet hair, aubergine eyes, and professional style—glasses perched neatly and hair secured in a ponytail. Her 55-kilogram frame and blood type A complement her disciplined nature, her birthday marked on April 21.

Dedicated to supporting struggling students, she hosts remedial classes where she initially dismisses the protagonist’s brazen request to view her breasts. Skeptical of his academic commitment, she proposes a challenge: improved grades in exchange for compliance. To her astonishment, he solves progressively intricate problems, defying her expectations. Forced to uphold her end of the bargain, she removes her top and bra, her composed facade giving way to flustered embarrassment as the encounter unfolds.