Hey Deadrop!
Every so often we'll drop some "Specials" that our Patreon backers can grab. These include things like a digital collection of art of the girls, custom animations, etc, that doesn't impact the actual game itself.
We do have some Patreon exclusive in-game dreams (which are side content), but everything else is available to all players.
The core game and a bunch of side content will always be free and available.