So I had the theory about the sister being autistic because of that one chapter in which she needed the mc to take her back home because she got lost just traveling down a station, which would explain why she is being an asshole to her sister too (Honjo herself is kind of a weirdo too, so they both could be on the spectrum)
But she may actually have deeper problems if her situation is this bad
Or maybe she is actually aware about the misconduct of those criminals, but her social deficit is getting in the way of her taking appropriate action, so the situation not only continues but escalates
This is also the second surprise rape chapter, author what the hell...