Kaori Saeki is a student at St. Walpurga Academy deeply fascinated by the occult. She leads the school's witchcraft club and learns of Taki Minase possessing the Bible Black grimoire. Her ambition drives her to seduce Minase in an attempt to acquire the book, though she ultimately fails. She then allies with the school nurse, Reika Kitami. Under Kitami's influence, Kaori is subjected to mind control and participates in rituals involving the kidnapping and abuse of fellow students and teachers. Years later, Kaori returns as a teacher at St. Walpurga Academy. She reforms the occult club with new students, aiming to restore the Bible Black's power. She again falls under Kitami's control, carrying out orders involving torture and sexual violence against enemies. After Kitami's defeat, Kaori abandons her pursuit of dark magic. She becomes a Makai Priestess, seeking redemption for her past actions by protecting the innocent. Her character evolves from an ambitious occult enthusiast to a remorseful figure attempting to atone for her crimes.