During summer vacation, the protagonist and his three female friends from the adventure club (Sahoto, Mei, and Chiyo) get carried away by the sea and wash up on a mysterious island in another world. The island, known as Haremun Island, is populated almost entirely by women (99% female) and is in decline. The village chief explains that the island’s guardian deity foresaw their arrival and that they must help revitalize the island into a thriving tourist destination so the deity can regain enough power to send them home. What starts as a survival and development mission quickly turns into a full harem paradise filled with passionate encounters as the group works to “develop” both the island and its eager female residents.