Sayuri Ookami, an 18-year-old third-year student at Kagome Academy, excels academically and maintains a model reputation among teachers and peers. Her distinctive violet hair and brown eyes accompany frequently rebellious modifications to her school uniform. Publicly respectable and disciplined, she privately harbors a possessive, manipulative nature, operating on a philosophy of taking desired things while meticulously avoiding exposure. Her primary motivation is an obsessive drive to exclusively possess Shinobu Handa.

To monopolize Shinobu, Sayuri first attempts seduction in an empty room, facing repeated, hesitant rejections due to Shinobu's reluctance to hurt others. Recognizing Shinobu's attachment to Momoko Naitou, Sayuri shifts tactics, plotting to provoke Momoko into violent, expellable behavior to remove her as a rival.

The execution and outcome of this plan differ between adaptations. In the manga, Sayuri's manipulation culminates in Momoko attacking her with a fire extinguisher. The incident is resolved out of court, allowing Momoko to remain, though she later transfers voluntarily. In the OVA, Sayuri physically confronts Momoko, punching her and inadvertently causing her to strike her head against a fire alarm, triggering a school-wide emergency. This results in Sayuri's expulsion from Kagome Academy, while Momoko departs by choice.

Despite Momoko's removal, Sayuri's plan ultimately fails. Four months after the incident, Shinobu and Momoko reunite and consummate their romantic feelings. Following her expulsion in the OVA continuity, Sayuri presumably transfers to another school.