Nope, sorry.
The game will be released for free, but maybe I'll add an option to donate.
There is a little bit of futa content in the upcoming sequel, though not for the main character. The reasons are two: first- every body transformation added to the MC is quite expensive development-time wise, so I can't add all the tf content I want; futa is not one of my main things, so I simply chose other stuff over it; second- I'm bad at drawing dicks :p (there's still gonna be some peepees in the sequel though - stay tuned!)
I just checked, since I didn't remember, and past me decided that bonus art is only unlockable with normal difficulty.
That's not great, if I did it today I'd definitely make it available in easy mode as well (in fact that'll be the case with the sequel), but that's how it works in this game unfortunately :/
I may release a demo at some point since the full game is taking so long to make. However I first need to fix at least the most problematic bugs and balance a bit the existing bosses before I can release anything vaguely enjoyable (the latest playtest revealed several issues I'm currently working to fix).
I'll try to get something out as soon as I can, but unfortunately no promises :c