I played a few rounds, it's pretty fun and I like the theming!
I think the cards would benefit from a Slay the Spire-type visual layout with text for effects and corner icons for both energy and damage. I found myself re-reading my hand a lot to sort out what damage and effects I could had.
In terms of the gameplay, I felt that the difficulty was balanced enough to be interesting without becoming frustrating. Paying attention to my moves I didn't have much trouble beating the three encounters, but I had the feeling that carelessness would be punished.
This seems like a really solid system to build a broader game structure on; I could see, for instance, choosing to play with a handicap in a certain fight to unlock a powerful card or getting curse cards that have double-edged effects.
Also, I'm interested to see how you build out the world and player character. I've seen a lot of good lewd fantasy settings recently (have you checked out Incase's GrimLewd works?) and I'd love to see the demons here have some more personality than the one-dimensional goon archetype they usually get stuck with. I recently read C.S. Lewis' The Screwtape Letters (odd material to bring up, I know) and I think he writes deliciously evil but logically thought-out demons in that tome. And who knows, maybe that could inspire some broader narrative aspirations, assuming you're into that sort of thing.
Overall, I'm excited to see where this project is headed, and you should definitely let me know if you're fishing for artists because I'd love to contribute to a project like this!