https://www.melonbooks.co.jp/detail/detail.php?product_id=2718019&adult_view=1
Scanned by me.

Synopsis:

A small island floating in the Sea of Japan.
Once a thriving port where fishermen would wait for favorable winds, the island has since fallen into ruin and become uninhabited — or so it is officially.

The protagonist, at a loss with a sudden windfall of money, spends a fortune to obtain a ticket to the island.
There, in a whole island reserved for a single guest, innocent young girls offer their hospitality. The destination: the so-called "Island of Prostitution."

Indulging himself in a world where only young girls exist amidst the nostalgic seaside townscape, the protagonist enjoys his carefree stay.
However, there is one unsettling tradition passed down on the island that weighs on his mind...

The second work from this duo of authors. Their first doujin was Anoko wa Boku ga Suki ja Nai (JP / EN).

Looks like they're going to release this work digitally after the second part comes out:
https://x.com/hagerock_salt/status/1869724901319573678

The last picture with character designs is also from the authors' Twitter:
https://x.com/hagerock_salt/status/1713122936734060937