The MCs Mother and Father die, so he goes back to the island where he grew up on and lives with his older female childhood friend. Turns out he is to become the new head of the village on the island.
So he does some ritual and drinks the blood of this goat/horse god being, and is led into a cave. His childhood friends shows up to comfort him, but a person/monster in a horse head mask shows up and kidnaps the the friend. The MC feels something fishy is going on in the island so he hires a new-reporter/investigator to help him find the truth. One of the island ppl decides to also help him, but is killed my a group of females wearing horse heads. Apparently the island is protected of a horse/goat god being, or something. anyway some stuff happens , and the childhood friend eats part of the god, she gains powers, rapes the MC and kills the village.

ring any bells? thanks

________________

Probably. haven't read it all so not sure.
Kyuusen no Shima

yes thank you

________________