Yumi Hayama teaches English at Seimei Academy. A prior rape by her ex-fiancé Matsunaga left her deeply distrustful of men. Vice Principal Ishiguro later drugged her at a faculty gathering intending assault; though she escaped, it reignited her trauma. Ishiguro then blackmailed her through a scheme involving student Katsutoshi Yoshioka, who lured her to an abandoned factory under false pretenses of a missing student. There, Ishiguro and associate Gondo restrained and repeatedly raped her while coercing Katsutoshi to film the assaults.

The recordings forced Yumi into sexual slavery under threats of exposure. Her tormentors imposed humiliating conditions: attending school without underwear while wearing a remote-controlled vibrator activated by Gondo during class, provoking a public breakdown. They escalated her degradation by compelling Katsutoshi to rape her despite his resistance.

Ishiguro expanded the blackmail, arranging her sexual exploitation by Board of Education members in a gang rape where Matsunaga reappeared and participated. This shattered Yumi’s remaining resolve, leading to emotional resignation. She instructed Katsutoshi to prioritize protecting Keiko Fujimura over rescuing her, accepting enslavement.

Katsutoshi later attempted to steal the incriminating tapes but was captured, resulting in Keiko’s forced involvement as punishment. Yumi’s reaction remains undocumented.

Physically, Yumi is 24 with waist-length black hair featuring side locks and blue eyes. She typically wears professional skirt suits or sweaters but is often forced into lingerie, slave collars, or public nudity. Initially kind, naive, refined, and religious, her personality eroded under prolonged abuse into fearful obedience and psychological detachment.