Isle of Fall

Satoshi and Mary are a couple in love. They were meant to spent a lovely summer together at a certain summer resort, along with Satoshi's uncle, Kendo... However, Kendo is unable to go, and their plans are cancelled.

Several months later, Satoshi receives an eerie email from his uncle. In it, Kendo explains how during the Fall season, the Naval Treasure Resort hosts a one-of-a-kind Test of Courage, at a nearby abandoned island. Couples who successfully complete this test are made to participate in a ritual, which is said to bind two people in love for all eternity. Feeling that his relationship with Mary is on the road to stagnation, Satoshi accepts the invitation.

Thus begins a kinky, fun-filled Halloween adventure for Satoshi and Mary, along with their friend Hanako and fellow couple Natsuki and Yoshi! Sexy costumes, sexy times, all alone in a deserted island!
...Or that's how it was meant to be.

[From F95Zone]