Keep watching: I skipped through ep.2 to see what happened
One-line summary: hardcore porn
It's based on an adult visual novel that previously got a hentai adaptation in 2014. It's also deeply scuzzy. A school trip went wrong when the ship crashed on a desert island and all the girls got infected with a virus that amplifies their sex drive and kills them if they don't receive semen.
"Why does semen taste this good?"
The only male survivor is fat and unpleasant. The "plot" in ep.1 is what you think it is, but ep.2 has some disturbing revelations. There's a (female) doctor who's doing all this as an experiment and also deliberately infected herself. She has a vaccine she's been keeping secret. In return, our hero chains her to a wall and maintains his harem king status with all the girls even after they've escaped from the island.
Frankly, it would have been less disturbing had everyone died.