I mean, depends on which definition of NTR you subscribe too here.
Can you prevent Kotone from getting fucked by other guys? Nope. That's basically the whole point of the story so to speak. she regularly gets fucked by other dudes until the story's over. So while in theory you only have to see one scene of that happening to her, in practice, every time a banquet happens, she's getting fucked by at least one person and that can't be prevented. The family is literally getting paid for it after all.
Can you prevent her from getting impregnated by other guys and turned into their wife or any such similar things where she's definitely taken away for real? Yes. Can you prevent her from falling in love with any other guy because of the overwhelming strength of their dick or whatnot? Also yes. Can you ensure that she becomes MC's wife or whatever? Absolutely yes.
So if your definition of NTR is the most literal one, aka "to be taken away by sleeping with", then yes, you can absolutely prevent the NTR. The "sleeping with" part can't be prevented, but that's the method through which she's taken away, not the result or end all be all of NTR. It's like theft prevention. If a thief tries to break through your door and damages, but fails to get in and steal anything, well, you still prevented the theft.
If, however, you're one of the people who subscribes to the "if the girl even looks at another guy's dick she's being NTRed" definition, well, I dunno what to tell ya bud. Just focus on the other too sloots? Though Saya IS married, so there's some scenes involving her having sex with her hubby and stuff. (So technically, MCs NTRs her away from her husband.) The only one who you can ensure never gets touched by another dude is Ririko.