Harem Isekai

Going to point out there are SEVERAL applications to “Size Control” that might involve Lust.

Hip ratio (for ease of passage in labor if you ever actually intend to add Pregnancy Content; it can also apply to the size of the hole in her pelvic bone, which is what actually matters in that regard) Her waist ratio – Or his Cock & or Balls (if you think either matter to virility; and they might help, but they might not necessarily) The elasticity of her pussy walls… You could even go with the really retarded “Vore” or “Giantess” content by making him shrink down, or enlarge her to the point where he might as well be tiny enough to see everything about the inside of her pussy [Not that she’d get much out of it. Other than maybe using his whole body as her actual dildo, while he jerks himself off inside of her? o.O ]

** It doesn’t speak well for your creativity that you say the ONLY option possible is just give X girl bigger tits.

There’s also the point that “Free Roam” implies Sandbox, which is going to dent your audience size.

“Prostitution” also isn’t really an attractive tag for a Harem Game. The POINT of Isekai is Power Fantasy; and the point of a Harem in another world is literally NOT to have to go and PAY a girl to fuck you, as the MC. : /