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)

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)

A summary of episodes 1-6. 1 hour of material cut out but 4 new scenes (7.5 minutes) added. 

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