itch.io

No, somewhere on itch you can look up your purchases, from their you can request a steam key.

You can find all of the VNs you have paid for on itch.io, by clicking on the downward facing character (looks like this '^' but faces down), to the right of your itch.io name, on the Main Page. Then, click on 'My Library', then click on 'Things You Own' and look through your bought VNs. Hope this helps.