Will the game also be released on Steam?
If so you will also get a Steam Key if you buy it via itch.io
We want it on Steam but Steam did not accept us due to the adult nature of the game. If you want an adult game on Steam you are basically playing Russian roulette and hope you get a nice reviewer/tester, we didn't... they usually give no second chances no matter if the reviewer's judgment was right or wrong, and even if you change things they don't even look at your game again. I know it sounds very silly but sadly that is how big company's like this work, happened to many other adult games. We are still trying to get on Steam but we don't know if they will ever allow the game on steam. It is really sad...
Itch is much nicer to developers than Steam is. Also Steam takes a whopping 30% of all sales, itch just takes 10% for doing the same thing. So honestly, they deserve the money much more. There is no big disadvantage in buying here, you can even add the game to the Steam library manually if you want to start it via Steam.
Well that's just Steam, I have no idea how Kagura Games manages to get the game on Steam maybe because they had the customized version from the beginning and you can just download the +18 patch for free from the Kagura Games website as a player.
This doesn't seem to be a problem on Steam.
For a few years now you can only install and play adult games/DLC via Steam Key on Steam if you live in Germany for example.
Thanks for the answer though.