I preaching this every time incest comes up, but maybe I my comments are too broad to help me get an answer I'm looking for.
So if you don't mind, I'll ask you personally.
Why do u feel "not sure" about incest kiss? What does it mean, "unsure"?
Are you "unsure" about murder? rape? pedophiles? cause all these themes are present in this manga, yet nobody seems "unsure" about those violent topics.
It's just incest that triggers everyone. Mangaka made sure to show it as socially unacceptable through kana and etc. What's to be unsure of?