This isn't some stupid romcom.
If the two of them want to fuck, they would just fuck. Personal baggage be damned.
You're 165 chapters in, how do you not understand this by now?
Remember the needle girl was out here getting raped day in day out repeatedly in the afterlife before they showed up on the flying ship and there was no quarrel whatsoever.
If you're actually pissed off about characters having sexual affairs without Kazuya then you should have dropped this manga a long long time ago.
Um not burst your bubble but many readers dropped when the shit with Shinobu happened. There was also an uproar with Oriobana getting raped
no insertion by the old guy.
"Muh NTR" has been called out each and everytime, you clearly don't follow Japanese tweeter to see how bad the pushback was.
Also "Kazuya drowning in pussy" is the most out of touch arguably moronic take, used to justify the NTR that took place. Sunao is part of the main girl team. It's like saying High school DXD, our main boy has Akemi taken away from him and fucked by another guy. LITERALLY same circumstances.
Also further sorry to burst another bubble but yes, a female NTRing the protagonist's main girl is arguably impactless cause the NTR most of the times (and certainly in this manga) does not get completed; the girl doesn't have her heart stolen and doesn't want to continue engaging. That's been the case here. But when Sunao becomes Kotetsu's bitch, I promise you it will permanent and her heart will be stolen. NTR complete.
So learn what NTR actually means, learn how the Japanese audience actually reacts, not just the westerners on Mangadex, those opinions don't count shit for the author, and then come back to Grace us with your shitty takes. Maybe they will be less shitty then