The author herself mentioned that the supposed "NTR scene" that you're talking about was all in Yutaka's own imagination and not reality. Author's tweet linked
here, and associated reddit discussion
here.
It's character development on his end, where we get to see him realize his feelings and wanting to protect Tsumiki, but also realizing the difference between human and genjin culture. (i.e, it's more normal for genjin to help other genjin out, they understand each other's characteristics)
The whole point of that chapter was that humans and genjin have different value/ cultural systems. What humans consider as an intimate act has little value for genjin. Yutaka realizes that at the end of the whole ordeal, and that's why he apologizes for his actions after. It's also hinted at that Tsumiki sort of realizes the difference too, but not explicitly.
There's literally been 0 instances where Tsumiki shows any sort of sexual attraction to anyone in the story outside of her current budding interest in Yutaka, and even that's only in it's initial stages.
It'd be wise not to spread false feelings on things that have been already disproven. Could the author have done it differently and perhaps a little more clearly? Yeah, but please seek help if this is all you see in a fluffy romance SoL, thanks.
