Love the game, the story is top notch and the characters well realised. Very human in their reasons for hentai debauchery.
Would love the ability to either antagonise or befriend Erin over the course of the game. A huffy fledgling to take under my wing and mold as his "wingman". Betrail by a guy who makes it hard to hate him would really add to the NTR sting.
I also would love to be able to pull him to the demon side with the promise of becoming the Alpha male he wishes to be, or atleast the alpha cock he always wanted. I want to have him join me in dicking down these mad demonic and holy goddesses (and their accolade, secret final boss Cecile) and show this world there's a third option. One where the chaos balances the order. Where loss is can be a possitive learning experience. Where the way of Mars can teach one how to grow into stronger men. Leave him the girl(s) you're less interested in maybe, knowing that they found pervy happiness. With Mars has continued access to her as the true Chad among Chads, of course.
In short I want to the girls to be able to control and help corrupt the little twink, via his new monster cock he doesn't have the will to control himself.
Even tho i find that idea to be the healthiest option for Erin, the reality is that Erin is so fundamentally fked genetically and was destined to be a cuck and a simp, that i would bet if you did that the Goddess would unironically doom the world.
But for any other characters NOT destined to suffer in such a way it could be possible, but the thing the game is showing is how Mars KNOWS how to fully please women better than any men in the game up to this point and it makes sense, the dude was groomed into being a manipulative seductor, even if Erin magically grew into a chad for some reason, the women would still prefer Mars, that is just how it is.
I would find more interesting that other guy was Mars wingman, but not Erin, Erin is so extremelly screwed by the Goddess, if you ever do something the Goddess doesnt like to him, its likely you just combust spontaneously.
Also im PRETTY sure Cecille cursing him completely destroyed Erin from ever becoming more masculine, if you read the lore, the dude is absolutely ruined.