Right? I think they minimised the toll that all those restraints would have on the character, let alone all the other shit he had done to him which even if it is "consensual" is still physical violence. The dominant character just went from 0-100 at their first meeting and hasn't showed much consideration since.
I wanted to say LMAOOOO but i cant bc it's true
Also it's worth considering why in some countries such activities like the ones shown would be viewed as illegal. For example, people cannot consent to actual bodily harm. The character here, has had at least 5 years of essentially being physically assaulted, so regardless of the legal definition his body is still being subjected to some pretty severe restraints and beatings which are going to take their toll. And yes, people getting permanently injured or dying is hardly unknown.
Kid, let adults talk here. Go read some more shitty mangas.
I think the criticism is that the story doesn't have much depth or character development. It's not the topic of BDSM which is drawing the more critical comments, but it's portrayal just seems to be on a "smut" level rather than using the opportunity to explain their relationship outside that "room" (think it's just known as the room, ha), their motivations, the after care yada yada.
If they keep doing this without a safe word, someone's going to die soon.
We know there have been many death cases involving bdsm. This is just how serious this shit is.