Loving the art style, and the story is decent! But, I feel like there's one big oversight in the story. I'm not an expert on storytelling or anything, but just my observation / opinion. And I'm sorry if someone else has already voiced this.
I feel like if I were to receive the modification the MC does, the first thing I would do when I got home (or even in the clinic's bathroom or something) would be to check myself out in a mirror. See for myself the difference the surgery made. But we don't get that in the story, and the next time we see the MC's member, it looks rather normal and not as big as I was expecting.
When he takes his clothes off in the lab, he looks to be maybe 4 inches long flaccid, which would probably then translate to 6/6.5 erect. A body modification like that, I would expect to see him 8/9 inches flaccid, and at least 12/14 inches erect. Yes, I know that's a ridiculous length, but this is a genetically modified penis in a porn game, so it's going to be ridiculous
Just thought I would throw that out there as a suggestion, since I think that would really drive home the story and give players context for what the women are seeing / desiring.
In addition, I like the info card that comes up when you meet a new woman, but it's unfortunate that you aren't able to find that anywhere else after that time. It would be nice to have a directory where you can revisit that info. Just a thought.
Anyway, thanks for the game - looks very promising, and I'm looking forward to see its progress!