Wut? Don't you mean tsundere? I'm more used to yanderes using violence against potential rivals, not their love interests. Either way, I suspect we can blame the guy that just came up to the house. And a bit of the mother for not being there for her as much, but she really didn't have much of a choice if she wanted to provide for her kid(s).
See above. Yeah, I'm basically saying it's parental issues. I said that in a previous chapter comments, too. I mean, the chapter where she was remembering her mother having to leave (and pointing out that her father is basically never there), and she kept repeating "Where are you going?" ... and later Miyamura corrected her that she should be saying "Don't leave me." The details are there, if one is to really go looking for them.
I was honestly watching that, and how Hori was getting more pissed, and I was internally screaming for him to stop inadvertently putting his foot in his mouth every time he mentioned that name. I realize he still needs to get used to telling the signs, and he's super awkward, though, so I don't really blame him, and I don't blame her because she can't help feeling insecure and it scrapes against her emotionally vulnerable heart. It's to be expected she'd instinctively, reflexively lash out. It's not healthy, but I understand it all the same. These two are just so broken and need to heal each other.
Like, yes, I know you are right, it's toxic, but it's a product of her upbringing, or lack thereof, I'm pretty sure. She needs help, not disdain. And not everyone is suitable to give that help, and that's okay.
I feel like this is true of just about every character that resorts to violence in these stories... so long as they are well-written characters with reasons for their emotional vulnerability, like a lack of good parental figures present in their lives, or a poor social life through most of their schooling... that sort of thing. (one of the most recent examples from my readings before this story had the double-whammy of both at the same time, where her mother grew distant and always traveled as she focused on her international corporate work and her father, though present, was probably busy managing his underworld organization, and said underworld organization had over-protective lieutenants that sabotaged her efforts to socialize in schools, so I found it understandable she would lash out like she did)
I've read my fair share of stories that have what I would classify as 'tsundere' female leads with understandable sources of emotional instability and vulnerability like I cited earlier. They all felt like such poor, vulnerable girls once I looked past their tough and often violently reactionary exteriors, and the male leads turned out to be just who they needed, with persistence, to help heal the scars on their hearts. Obviously, trying to 'fix' people isn't necessarily a good idea, but it makes for a good fantasy to have love remedy emotional scars.