In'yoku Oujo

The lake which they happened to use as a rest-stop turned out to be a tentacle monster den.
This CG novel tells the story of how Le*sz is soaked in tentacle monster fluid which turns out to be an aphrodisiac, and she gradually loses all sense of reason in her growing desire.

The fate of Le*sz rests in your hands as you make decisions in the game!

[From DLsite English]