It's a great game! It's really entertaining and easy to understand for someone like me who doesn't know much about the series it's based on. The art is very pleasing to the eye, and I like the scenes more for the work behind them than for the sexual content; even the fact that there are animations is something to admire.
Personally, I think a gallery where you can see the scenes would be a good addition, since in this type of game it's annoying to have to save the game the moment you think a scene is coming up.
On the other hand, it's clear that the game is designed to have different routes where you play as a sinner or someone trying to restrain themselves. In that case, something like a karma warning or something similar would be appropriate; the player would be clear about what they're doing, and it would combine well with a possible gallery explaining that some scenes are only available in one route or another.
Perhaps it would be appropriate for the gameplay to shift at certain points to something akin to a "command center" where you can interact with the characters independently of the visual novel. I'm not asking for the game to be solely about interacting to gain trust and trigger scenes, but a bit more interaction beyond dialogue choices would be welcome. This could perhaps lead to clothing choices, special scenes, or something similar.
One detail that I know might be a lot to ask, but would be fun, is the ability to choose the protagonist's appearance. I'm not referring to a character editor, but perhaps when we see our reflection, the question of what we want to be is asked, changing the illustration when we see our face. It would simply be a small detail for that moment without making changing dialogue more laborious, as the dialogue would be neutral to your race, so to speak. Even so, I know it's a complicated addition due to the whole issue of illustrations and everything else.
I must say, you're doing a great job with the game! Take your time to polish what you see as necessary and add whatever you think is appropriate. I hope this project succeeds and that you achieve all the goals you have set for it.