The NTR seems more satirical commentary than actual gameplay to me...the "rival" is literally a super-creep and when he has interaction with the MC he tells him "see boy, you're just like me after all"...his "seduction" methods are basically creeper methods...combined with things like the commentary before the mom's door at night, it's basically a critique of the standard "teen creeper" game setup. The women have a degree of agency, value their privacy, consent is important and the MC has some degree of ethics. While the rival does not, but is relatively easily thwarted. The rival stays in the picture to serve as a moral "warning" to the MC, to think through the consequences of pursuing the women in the household.