One of the things I like about Katsura is his willingness to get very dark with his comics. I don't feel like this one went too far, I do however think it lacked the proper buildup. We get a character who basically becomes a rat with an orgasm button, and it's disturbing to see the lengths that it's taken. There is also a case of a female character being slapped by a guy, and while I acknowledge this manga is a couple decades old now, it's VERY shocking to see that not be a bigger deal.
The one other issue I had with this one is that it fell into one of the worst ecchi/romance cliches: the inexplicably bad timing. It was abused in this volume, being the source of almost all conflict spread across several different incidents. It removes character agency.
Edit: I rated this four stars initially but mostly only mentioned my issues with it. On re-read I really like what we get with Yota, Moemi, and Ai, and it's good to still get some of Nobuko's POV too, she actually has a pretty interesting subplot going on. Also, I was more okay with the timing this go around, I guess mostly because I realize I've seen it abused much worse, and it's made pretty good use of here.