You know, I'm not exactly big on NTR myself, but damn if it doesn't feel like with every year that passes, NTR haters invent more and more sub-categories and stuff just so they have more things to complain about.
The whole thing started with stealing a girl/guy from someone in an actual relationship, usually a sexually active one or one which had the promise of becoming sexually active. And it was actually stealing that person, to the point where they completely abandoned their original partner and stopped caring from them completely. Often enough it involved an obsession with dick and the original partner being poorly endowed or bad in bed or something, because of course.
Nowadays, there doesn't even need to be any kind of relationship at all. If it's not complete monogamy, then it's clearly NTR.
By that logic, harem eroges are NTR, because the MC isn't loyal to any one partner. Albeit, it's not from the player's perspective, but clearly, it should be tagged as such.
By that logic, this game is NTR from the other angle as well, with the MC wanting to take the girl for himself and all her other partners, who had her first, in spite of the fact that he only learned about her recently. Or more like the player rather than the MC, but still.
Like. Seriously. Everything that isn't perfectly monogamous is NTR by the logic above. Which is stupid.
NTR is more than just a lack of faithfulness. It's a matter of intentionally causing someone else emotional harm. At its core, the whole thing about NTR isn't just about stealing the guy/girl/whatever. It's about emotionally destroying the person that this is being done too.
How does ANY of that apply to this supposed sub-genre that seems to exist just to get people offended. How does it apply to this game specifically when the girl makes it clear that she's a slut that fucks anything with a dick that can satisfy her? No one's trying to emotionally harm the MC, and only an idiot would try to get in a serious relationship with a nympho like that unless they were able to accept that she'd never be exclusive to them or anyone.
But whatever, tag everything as NTR, until the term itself loses all meaning.