I don't usually comment on these. The Internet is a sea of pornography, and if you don't like where you're floating, just hoist anchor, set sail, and drift on to more fertile waters. That's how it's supposed to go... but, sometimes, something comes along that gives one pause.
Starting in on this, my expectations were not great; main character contrived into a fantastical world, unexplained conveniences, and a deuteragonist that, visually, was not, at first blush, appealing. But it was only proper to give it a fair shot, so I pressed on, and... well, wow!
First of all, Ehrlynn's design. Being a succubus it would make sense that she had an almost uncanny-valley sort of inhuman structure; the chin, the cheekbones, the eyes... and the old-fashioned up-do is not something one sees everyday, so that too just made the whole character seem a bit ... off. But, here's the thing about characters: they are a lot more than what they look like. Or, they should be; all too often they aren't, and a clever audience is immediately going to expect a clichéd trope. So when the MC called Ehrlynn a 'demon' and she pointed out that the term is old fashioned and a bit bigoted, BAM! Expectation subversion. And it just got better when the MC showed concern over their actions in bed, and Ehrlynn showed patient effort in trying to comfort them. That's a character with heart, and that matters. Oh boy does that matter. Anyone can smoosh a buzzy to their tingly bits and pop out a 'gasm, but having an emotional investment just makes it a thousand times better. And when that emotional investment was made... the appearance of the character seemed to change. I was no longer looking at a character model; I was looking at a character. And suddenly she became beautiful.
And then I started to notice other tiny details. Like, not ever seeing the MC's eyes, and giving her a short haircut. This pushed the MC toward androgyny, which helps to imprint the player upon her. This is the same trick knowingly used in the Legend of Zelda games; by not giving Link a voice, they're letting the player give Link their own voice. I also appreciated that the introduction to the world was also a soft introduction into the mechanics; a way to declare preferences for what would become a much more expansive game, and that it was done diegetically.
That's not to mention the most excellent renders with subtle emotions in the facial expressions (which I'm very glad to see did not drift into excessive exaggeration)
If I were to suggest a way forward, I would say, Uncle Aaron from 'Into the Spider-Verse' said it best: "You're on your way. Just keep going."
If you have any fetishes that you'd like to put into the game, don't hesitate. You can always put in a warning before the scene, as you've already done, and that should cover it. Though, if you can figure out how to do it in such a medium, I'd suggest looking into the psychic link between Ehrlynn and the MC a bit more; that sort of connection could really, really elevate sex to a new level... especially if they can see what the other see and feel what the other feels.
Sorry if that was a bit rambly, but, yeah. Loved it. Can't wait for the update!