In the prequel, theirs wasn't an established relationship so Kishibe's obsessive behavior is quite questionable in that the author is trying too hard to portray him as obssessive and borderline psychopathic without any real stakes (compared to characters in the works of Harada, Ogawa Chise or Psyche Delico, that is). So this sequel, when Kuroiwa's level of desire has matched Kishibe's freakequency, everything is all fine and well - they're just a sex-crazed couple with really jacked physique. The story isn't going to be held in high regards plotwise, but the setup for the readers to end up in their bedroom at the end ofevery chapter is actually quite satisfactory. Like yeah I suppose it would probably feel exhilarating to experience some sort of dynamics like that with your bf/gf.

And the elaboration on their past feelings is quite alright - Like sure, if I spent 20 years pining for someone like Kishibe did, watching Kuroiwa's every movement, every phase of life, every passing relationship, I wouldn't be able to hold myself back from clinging onto them for dear life either, right when the feelings are finally reciprocated. But what are the odds, lol? Thank god manga artists turned these sentiments into stories so people can still get a taste without suffering so much themselves.

So in short, the manga is splendid to vicariously relieve one's desires. It's convincing. It's ravishing. It's not (that) off-putting (anymore). It's not trying to be too ambitious. Just hot characters having nasty good sex - there's all to it.