Kemono to Ore no Kodzukuri Chakushou Nikki ~Mukashi Tasuketa Kemono ni Ongaeshi de Tanetsuke Saremashita~

Yurito, a playboy who attends veterinary school, is suffering from being "avoided and hated by males", whether they are humans or animals. While he has a wild sexual life with women, they can't fully help him, so he has to do it himself. One night, when masturbating, a big black beast shows up all of a sudden and licks him there!? On top of that, the beast turns into a human and says, "You saved me a long time ago, and to return the favor, you'll conceive my child." After that, the beast who claims to be a god pushes him down and rubs him in the spot that even he can't reach, and it feels so good...!!! (Source: Coolmic)