What would the Japanese police do in this situation if she actually went to the cops? In America at least they would consider this a serious assault and Mao would be immediately visited by police and I think it would be the same in JP. Also I feel like the reactions from the other women are strangely subdued and not realistic. I find it hard to believe that no one would file a report or bring her to the police.
Well, I don't know what the Japanese police were actually like in 2012, but firstly, note that you don't actually have that many named characters present. Yamada already
is telling her to go to the cops because it's serious; Momo has already been repeatedly shown to be a "Hell, no, I'm not getting emotionally involved in
anything, what's the point" type of person; Kokoro's already been shown to be all talk, no action, and she'd presumably be terrified of getting sucked into proceedings and having her career at the club outed to her parents; and the boss would presumably prefer not to be directly involved in case the cops start asking why he chose to employ her in the first place.
Also I would suggest you're being a bit optimistic saying "Why are they not calling the authorities? Any police response would automatically take this deadly seriously and sort everything out."
Some would, I'm sure; every country's got at least some cops who genuinely want to help and have the training and commitment to treat these situations with respect. But, well, pretty sure a lot of women the world over still don't trust the police in situations like this right
now, let alone thirteen years ago. There's a reason counselling and refuges and whatnot exist, right? Plus we're plainly shown that Mii-chan is right on the edge of saying "No, no, I don't want to press charges, don't arrest him, it was my fault, we'll patch this up ourselves, get out" and as Momo says, that makes it all the more likely that even a well-meaning officer might think, even subconsciously "What's the point of putting too much effort into this? It's clearly just going to happen again".
I have no personal experience with anything like this, so if anyone wants to go "No, I can show evidence it's not that bad" or "...actually, it's worse", please go ahead. Just wanted to say, none of it struck me as that unbelievable or implausible. 🤷♂️