The game has a free adult patch that you can get on Steam : https://store.steampowered.com/app/2261480/The_Symbiant__Adult_Patch/
If you get an error when accessing the link, it means one of the 2 possibilities :
1 - You did not enable sexual content in your account settings
2 - You currently reside in Germany, China, Korea, UK or another country where adult content is banned
If you are in the second scenario, then you can get the free adult patch in this very page: look for "Adult Patch for STEAM" under the "Download Demo" section. You will then have to place the file in /TheSymbiant/game/adultpatch.rpa