Kaori Saeki attended St. Walpurga Academy, recognized for her intense fascination with occult practices. She often read costly black magic textbooks during recess and borrowed occult materials from the library. Her appearance featured long blond hair in a voluminous ponytail with side locks and striking violet eyes. As a student, she wore the school uniform, a black robe for witchcraft club sessions, a swimsuit at the pool, or casual clothes comprising a sleeveless white top, black miniskirt, and thigh-high stockings.

She led a witchcraft club with students Jun and Maki, convening in a rented apartment for rituals, including Sabbath observances. Her activities included conducting tarot readings for classmates Ayumi Murai and Mika Ito, which grew popular despite occasional inaccuracies overshadowed by genuine magic. She resided near the academy in a modern house, potentially with parents, housing a room cluttered with occult publications and magical trinkets.

After witnessing classmate Taki Minase execute successful love spells, she resolved to acquire his "Bible Black" grimoire. She seduced Minase at her home, trading sexual favors for book intelligence. Later, she invited him to a club meeting, but he arrived with school nurse Reika Kitami. Kitami overpowered Saeki’s group, magically inducing uncontrollable arousal before raping them and performing a baptism ritual that enslaved them under permanent mental domination.

Under Kitami’s command, she harvested semen from virgin males at school through seduction, ingested a ritual potion temporarily granting her two phalluses for intercourse with Jun and Maki, assisted in kidnapping art teacher Hiroko Takashiro via stun gun, and facilitated the abduction and drugging of Kurumi Imari. She coerced Minase into non-consensual acts with Imari before expelling him. She later helped orchestrate sexual rituals in the school basement preceding Walpurgis Night.

Post-Walpurgis, she discovered the Bible Black in the basement but was confronted by Kurumi Imari—revealed as Kitami in disguise—who incinerated the book and raped her. She subsequently performed a sexual ritual on Imari to transfer Kitami’s essence back into her body.

Years later, she returned to the academy as a teacher, dressed in a grey undershirt, lavender miniskirt, purple scarf, brown heels, and long white coat. She revived the witchcraft club with new students, targeting the Spear of Longinus and Bible Black’s restoration. Initial failures included a disrupted ritual and an unsuccessful seduction of teacher Yoshitani. After drugging and copulating with Vice-Principal Oshima, Kitami (as Imari) interrupted the ritual using the Spear of Longinus and reasserted control over Saeki and her coven.

Again subjugated by Kitami, she kidnapped former classmate Rika Shiraki—now a substitute teacher—and supervised her torture and repeated rape. She obeyed orders to engage in intercourse with possessed investigator Naoto Yamanishi, enduring violent assault when demonic forces overwhelmed him. She participated in torturing exposed spy Yuki Toudou, mocking and assaulting her while compelling Shiraki to join the abuse.

During Kitami’s final basement ritual, she pleasured her mistress before being dispatched to retrieve Yamanishi. En route, Jody Crowley sexually violated her and imposed mental domination, turning her against Kitami. She restrained Kitami during Jody’s ritual interruption, resulting in her bondage alongside others for the Ritual of Coronzon, where invasive devices penetrated them vaginally to channel dark energy. Tokken agents and Hiroko Takashiro freed her after defeating Jody.

Following Kitami’s permanent downfall, she renounced the occult and became a Makai Priestess, pledging to protect innocents while expressing remorse for past transgressions.