I'm looking for the name of a Manga. I remember the first chapter pretty well, and a few more specific details. Thanks in advance.

It begins with a college student traveling to an island with his class. They went to that island because a girl in the glass, whom the MC likes, was a native. A professor and other students ate there with them. After they reach the island, it starts raining and the students are shot by the natives one by one. Apparently, there was a festival going on at the island and it outsiders could not be present during it.

Every inhabitant of the island is immortal. The island is funded by prostitution, with girls trapped in a massive prison complex to be sold. The ring leader is an immortal lol who is married to the MC.

If anyone can help me out it would be greatly appreciated.