Ms. Yui is a tomboyish teacher who always wears tracksuits and nags at the dumb male students. Her students laugh at her behind her back, saying things like, "She definitely doesn't have a boyfriend," "She's probably a virgin," and "She's completely missed her chance to get married." However, her true nature is that she has a stronger sex drive than most, and she is a total pervert who enjoys exposing herself and masturbating in the school during class or after school when no one is around.