Personally I think that many things that are currently in the game should be improved:
-First of all the situation around Rita: I have to say that it's pure nonsense, what I mean is, you live in the village but you don't notice anything, however a stranger in the next city gives you a comment about the innkeeper and suddenly you find him trying to have sex with your sister.
Overall I don't feel it's a decent development, first of all what we should understand is why Rita can't leave her job at the inn if she is under that situation and she isn't accepting it, there could be 2 keys be it blackmail or debt, because if not she would just leave the job.
On another point that you don't find any rumours or notice something as your character during the time you live in the village is plainly weird, even more it would be hard for your sister to hide it if you talked to her about her job or showed some interest in how is she doing.
What would make more sense is that the situation was gradual since day 1 and keeps scalating, having to talk with her and trying to solve the issue before it's too late, basically it makes more sense like that and if you want to add a few scenes let the voyeurism be there, being able to spy on it.
-Then we have the priest: Overall what we did is really wrong, there should have been more ways to solve the situation and manage to bed her, the use of the potion is literally like saying "you are now the village bitch", I think alternative options to manage to get her in bed would be quite nice, perhaps after the kiss you could just increase your charm to level 3 and tell her you love her and want to keep seeing her smile, something charming, then she could want to push the limits a bit and under the passion ends up having sex with you.
The potion seems just like the fast reward option but with consequences.
-On another point there is the current stat system, which is basically charm (submissive) vs stud (dominant). However I just see them as ways to solve situations rather than definite attributes for dominance/submissiveness, it would make more sense to separate that part of the concept and make it independent (basically charm and stud becomes just ways to solve situations and dominant/submissiveness is more related to what type of scenes you are getting, or choosing at the start).
-Related to the main character it could be good to start defining his fetishes based on our scenes choices, basically that his performance on certain sex acts increases the more experience he has on them, being able to please more his partners thanks to it and giving it some use.
I believe we agree that a virgin isn't as good as sex than a very experienced man and our MC must have been a virgin before he met the succubus.
That's about it, I believe many missions need to make more sense compared to the current situation and to feel some kind of progress on our sex skills, for the rest... truly wishing to meet the other succubus and the initial witch that sealed her.