Tentacle and Witches (2011)

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.