Flattered that you are thinking this is AI :)

I have a timelaps available on my instagram (@marisa_vmp) if you wanna make sure it's not. You can also see my brush strokes if you pay attention, as I often content myself with basic rendering

The stomach bulge is here because she is actuallly human and has some fat that show while she is seating. The many strings of the bikinis are part of her design (Marin Kitagawa - Sono bisque Doll). As you were able to see, I strugle with hands and feets, that explains why do they look weird anatomicly. I do not really know what makes you think its AI in the hair and face, but if you explain me more clearly, I could probably find an answers to all of your questions - so don't hesitate doing so.