To enhance the game, I believe adding actually drawn background characters would make a significant difference. Currently, the game feels too isolated, with only the main characters present. This is particularly odd for a game that relies heavily on exhibitionism to drive the story.
Having played the game multiple times, I've noticed a few flaws, but the most glaring issue is the emptiness of the world. It feels strange that only the main characters exist.
For example, in the final part where they meet the super-rich guy who throws a toga party, the route where the girl gets painted is the only section that feels populated. However, even then, the lack of drawn characters makes it feel incomplete and strange.
Adding more background characters would create a more immersive and believable world. Add them everywhere as part of the background, and specially in those moments when the exhibitionism sections are triggered have the background characters interacting with such scenes as well, such as staring at the situation, running away, attempting to grope the girls, approaching to see from a closer distance and muttering a few words of excitement, disgust, annoyance, hornyness, or have them take a picture of the girl and let the main characters choose how to behave now that the situation has changed, etc etc.
You can play a lot with this. And it's going to significantly improve the experience of the player.
By the way, I decided to start supporting you after playing this game a couple times. I believe your work and your skills are well worth it.