Uji Keijin

Based on the game by Black Lilith. People moved to space, public order and security was maintained by the space federal managed by various species including humans. The lead character Iris and her partner Mei Ling are the ace pilots of the 101 special unit, belonging to the federal army SSF. During one of the battles, Iris is captured and taken to the whorehouse on Mirion, a city ruled by the enemy forces. She is forced to have a devil's collar around her neck which blows up if she attempts to escape.

Dark existences were secretly invading Tokyo, the diabolic city. Behind the success of ninjas of justice called Taimanin, the darkness starts the action... Hell knight Ingrid revealed the betrayal of a diabolic doctor, Sabato Kiryuu, who has belonged to a group of darkness, Kanomado. She follows after him who managed to escape from the spot. However, she gets the counterattack from Kiryuu in a certain hideous church and becomes captive. With vengeance, Kiryuu tries to destroy Ingrid's noble soul and decoy her boss, Edwin Black the vampire, into coming to save her. He encourages a group of monsters who have the desire for revenge against Ingrid to disgrace her body... (Source: DLsite)

As punishment for peeping on the busty witch Ms. Yuko, Ichiro Tachibana is mistakenly turned into a tentacled monster by apprentice witch Lily Ramses Futaba. Now in order to survive he needs to absorb energy directly from witches by having sex and filling them with his seed. Luckily, two witches are willing, knowing that if he doesn't he may go berserk and attack other girls.