You're reading this manga but still saying shit like this?How did the sister not only beat up that guy, but do so easily? Women are physically weaker than men. Both in real life, and in this fictional universe. We've seen this in universe with Mahiro, after becoming a girl. Unless the sister took some new experimental drug to temporarily become a guy, I call bullshit on her beating up those guys.
I get that women beating up men is a very old comedy trope in manga. But it makes no sense in this universe.