What's this? Actual kink in a doujin that isn't just vanilla or abuse pretending to be kink? And they communicate their feelings? Hell this is just one prenegociation of limits and safe words from being an actually healthy portal of bdsm. Who knew it could actually show up in a doujin!

Yeah, or they turn NTR. Type-G and his Lyrical Nanoha stuff is a good example of the latter. I met him through One Room, and he then made Mating Dance and the tone difference give whiplash. A good example for yours is Tachibana-san's Circumstances, mainly the second book/chapter/whatever; scenes where amazing but it literally hurt me to read.

Not really. The whole "harem plan" series has been pretty wholesome, at least until that last part where they join in together. And Trouble Teachers; the first few were...well not necessarily wholesome where pretty tame. But the last two chapters though.