That bitch is so...Just because she has father issues, she decides to take it out on random guy she meets. Her reasoning: I test his strength to see if he is trustworthy, but in reality I just want to beat him up, because I'm already convinced, that I'm stronger than him anyway.
In MC's shoes, the moment she would have pointed that sword at me, I'd give her a stern warning, tell her, that I hate battle junkies and that I give no f*cks about her reasons. Then I give her a chance to stand down. (I know, I'm naive and too kind. Most people would have engaged her in mortal combat the moment she tried to point that sword tip at their throat.) And if she doesn't I'd brutalize her, to set her head straight about attacking your allies, no matter what that sister of hers might think about me. And if she is stronger than me, I'd use unhanded tricks or run. And if she still defeats me, I'd refuse to work with her again(, if I'm still alive). I'd refuse to work with her ever again, no matter which case. No matter if I look like a sour loser or a brutal thug. No way in hell, I'd make up with her. Damn dangerous freak.
It's sad that the story went this way. This behaviour of the MC only works, because it is "That kind of story". You know: All girls are stupid bimbos and he as a male has to be nice to them, so that they have the chance to ultimately fall for him. It breaks any immersion, if any was left. Bad story telling. Immersive stories, yield more likeable/relatable characters, which in turn are more alluring/sexy, if that is, what the author was going for.
That mithril suite for girls is a bit sparse on the material. Why do males enjoy better protection. If that suite would be a thing, most females would buy the male version. Again something, that breaks immersion for bland fanservice.
BTW: Isn't it too Obvious, that her father has been framed? I know she was a child and it is a trauma, but now she is an adult. You'd think she'd call her memories and the whole story into question, before threatening unknown people.