Just finished my first playthrough of it. I am really enjoying the work so far. Just going to list my initial thoughts.
Bugs-I didn't spot many and the ones I did spot weren't that bad.
When Nemona is in the village wanting to bang some of the Chapter 1 girls, if you select 'Nevermind' it actually brings you to the Nami/Robin scene.
If you revisit the pond Serena bathed in and click on the same spot, then you can watch her bathing even though she technically isn't there.
Compliments
I love that you put in a lot of shortcuts or skippable content into the game. I'm the type that likes to experience the build-up to the porn, but I think it is good that you are accommodating to the people that want to move at a much faster pace.
Post Corruption Content
I've seen a few other people comment on the lack of content for the girls after their final corruption scene, and I have to agree with them. I like revisiting the girls, and it helps to hammer in the idea that they are fully dedicated to you. I think there are a few options we can add for post corruption content.
You can select one of your girls to be on "Wakeup Blowjob" duty.
Once you unlock a costume you can unlock the option to make the same/similar costume for a couple other girls. IE after finishing Nemona's quest you can give her bunny girl costume to Izumi and Sakura now as well.
Similar to the costume idea, maybe you could reuse some of these drugs to get a different experience out of other girls.
I don't know how easy it is to do this with your programming tools, not going to pretend I have experience with that, but you could give the illusion of more scenes by just taking one girl's sex scene and model swap for a different girl. Some people might not like it, but I would be fine with it as long as the duplicates are kept to post corruption scenes.
I would suggest maybe taking the time implement a few scenes like these after you finish Chapter 3, but before you start Chapter 4. You don't have to go crazy and add stuff for each girl. Maybe add a few scenes for a few girls after you finish each Chapter.
Other Suggestions.
This is probably more of a personal preference, but I preferred to get Naruto to go to the full Naruko transformation. Like have a scene where Lazuli pulls out the gender change drugs and asks Naruto if he would take it and fully commit to being a bitch.
I feel like Ino needs more content. She and Nemona and very similar as they both act as buddy your recruit for 3some/4somes, but you never get a scene of you just fucking Ino while she is in her own body and her crumbling to you.
Other
You just straight up stole a scene from a Sahara Wataru doujinshi. No complaints there. 10/10 decision.