Minase, a high school student living under the care of his cousin and guardian Yukiko, shares a sibling-like bond with her despite their lack of blood ties. His closest confidante is Kurumi Imari, a childhood friend and neighbor who aids him in daily tasks and co-leads the school’s art club as its vice-president. Though both briefly trained in Shorinji Kempo during their youth, Minase abandoned the discipline earlier than Imari.

His life shifts when he uncovers the occult tome "Bible Black" in the school basement. Recruiting Yukiko’s linguistic skills to decipher its French and Latin passages, he dismisses initial doubts and begins testing its spells—weaving magical influence over classmates like Rika Shiraki and Ayumi Murai. This attracts Reika Kitami, the school nurse and a shadowy sorceress tied to a disbanded coven. She subdues him through sexual manipulation, implanting a demonic entity that amplifies his magic while binding him to her will.

Compelled by Kitami, Minase unintentionally curses Yukiko with relentless arousal and aids in exploiting peers, including the brutal torture of art teacher Hiroko Takashiro. Imari’s violent intervention shatters Kitami’s control, spurring Minase to resist further corruption. Partnering with Takashiro—versed in counter-magic—he disrupts Kitami’s ritual to transplant her soul into Imari’s body, resulting in the nurse’s physical death while her spirit lingers within Imari.

Later media obscures his fate, hinting at a possible offscreen demise or alternate outcomes. The original visual novel branches into divergent conclusions, such as Shiraki killing him during a clash. Post-conflict, his bond with Imari deepens into romance, though Kitami’s residual presence strains their connection.

His arc spans multiple endings shaped by player choices, from redemption to eternal enslavement by dark forces. While his direct role in sequels diminishes, his choices ripple through prequel and sequel events, often echoed in secondary characters’ dialogues.