I think if I was writing it I'd focus on that sort of baffling helpless feeling. Like, usually NTR from the MMC's point of view is helplessness in the face of a superior force, if you follow. And one of the feelings will be a confused betrayal stemming from "your" entire relationship suddenly meaning nothing in the face of the simple primal sex act. You've done everything right, loved her, built a life with her, been true and loving for years, and she's leaving for a big dick? Really? And nothing of your life together is more important to her? There's literally no way to keep her just because he can fuck???
Flip it on its head and look for the same emotions. You've done everything you were supposed to- played football, built your body, dominated weaker men, "won" in every way, and she's slipping away because this little fucker knows the difference between second and third wave feminism??? Because he likes Taylor Swift? He drives a fucking Corolla and doesn't even LIFT! How can this be happening???
So you summon the same emotions with the game. Write some scenes where people see her interacting with the invader, but again, flipped. Where you would usually write their obvious physical attraction and the nemesis' physical dominance, now the humiliation comes from her very obviously connecting with the other guy in a way your meaty head will never be able to copy. Instead of waking up in the middle of the night to hear them fucking, the MMC wakes up in the middle of the night and they're in their eighth hour of talking about chick flicks, sitting on the couch all animated and laughing and connecting in a way you can't stop.
For the sex scenes, you could show the MMC fucking her hard like a proper alpha, then when the antagonist gets his shot don't even have him use his dick. Have him kiss and pet her until she's going crazy, then make her cum with his fingers. And then, since fingers don't have a refractory period, immediately do it again. Could make a pretty sexy scene out of a dude showing a woman new heights of pleasure the way other women do it, with fingers and mouth and toys.
And then flip the usual FMC transformation. Show her dressing super sexy for the alpha at first, then as she bonds with the nerdy nemesis have her stop dying her hair and wearing booty shorts or whatever and end up looking like this game's FMC in the cover shot. Let her discovery of herself mean becoming a nerdy dream girl as opposed to a hypersexed Barbie doll.
I think you'd want to make the MMC sympathetic by making him a muscly dude of the type we play in games. Batman gets cucked, basically. Otherwise the audience would sympathize with the antagonist, seeing as how we're all a bunch of nerds. But you could probably do it.
Fuck, now I wish I had artistic skills. I might actually try to write this story for my Lit page.
Edit: I can't type.
