Yeah, I know of one. I don't remember the name though. It's like this except instead of fantasy, the MC is cosplaying a delinquent from a manga. He only had one volume of that manga and the delinquent he's cosplaying seems like this tough, righteous bro in his eyes.
The thing is that the manga artist for that same manga he likes also made NTR using that character. He doesn't know this until the main female love interest shows the NTR manga to the MC.
If you pay attention to her behavior then you'll notice that her obsession with NTR is ACTUALLY a cry for help. As it turns out, she has a male childhood friend that seems normal on the surface but is a sick, twisted, vile, possessive, perverted, stalking creep.
He's the sort of guy that would most definitely wait until they were adults before drugging her, raping her and gaslighting everyone into thinking she has a nightmare before doing again at the next opportunity.
To protect her, the MC behaves like an NTR character to have this guy give up on her.
The MC then realizes that he can use this to save other girls from similar dates.
So, he basically became an NTR hero.
I'll try to find the name for it and get back to you.

Anyone know of similar things like this? Where either the Mc doesn’t wanna NTR people, or is an absolute scumbag who wants to be the girl getting clapped and stolen from her man like “ TS Tensei Bishoujo Netora Reiko wa Netoraretai”?