A school nurse who is possessed by a demon, and uses her powers to control the students.

(Source: animevice.com) 

Based on the erotic game by Active. 
Minase, a high school student, found a book of magic in an isolated room in his school. He started practicing black magic that has extreme sexual effects that benefited him and some of his friends. Intrigued, Minase got deeper and deeper into using the craft, not realizing the evils that will come forth. Eventually, the origins of the book was revealed, and so did the incident twelve years ago on the night of the Walpurgis, the night when the power of evil is at its strongest. After coming to his senses, Minase struggles to get himself out of the darkness that he had put himself into.
 
(Source: Anime News Network)

Based on the erotic game by Active. 
Twelve years prior to it's discovery by Minase, the origins of the magic book with dark,sensuous powers is revealed. Initially owned by a female student, Takashiro, who, along with other curious students form the first magic club on campus. The club begins to use the erotic spells to carry out favors for fellow students, and vengeance. After underestimating the powers behind the book, Takashiro is taken out of the picture, as a new leader guides the club towards a darker course, one that will force school newcomer Kitami to make a dire choice.

Based on the erotic game by Active. 
Several years have passed since the Walpugis Night incident and several bizarre serial murder cases have occured in the metropolitan area. Dead bodies of couples are discovered murdered during sexual intercourse. The women didn't have any external injuries, but the men were completely burned and carbonized except one part... their genitals. To solve these bizarre incidents, a special detective team called "Tokken" is deployed. Included amongst the members of Tokken is Imari who had experienced the events of Walpugis Night. While investigating the incident, they found a mysterious phrase, "Spear of Longinus," and a strange cult group that is related to the incidents.
 
(Source: Anime News Network)

Reika Kitami