@duylinh
It’s kinda obvious even without reading ahead. For the most part, Haru’s just complaining. Like most teenage girls would when things don’t go their way. Edit: Nay, like any reasonable person when unreasonableness and unfairness shows its ugly face.
Even if she could kill that guy, he’s the son of a very powerful guild master in town. Even if they couldn’t harm Haru in retaliation directly, they’re clearly strong enough that very few people would even want to go to war against them.
To act selfishly now would put everyone at the brothel at risk. Therefore, Haru cannot intervene more than she already has, as what she’s been doing has been within the rules of what’s socially acceptable, even if the way she and others are being treated is clearly immoral or unethical to us. This misogynistic world has rules that Haru regrettably has to play by.
That’s why, it’s a different case if
someone else were to come to her rescue, because the police or army certainly won’t. Chiba self-proclaims himself as the most reliable person around, but aside from contributing to sales, he’s effectively useless. He’s never there to walk the walk, never around when he’s really needed as a “reliable man to protect me”. As a man in that world’s society, Chiba has strengths on virtue of being male that Haru doesn’t have. In Haru’s mind, he’s someone somewhat useful to keep around, but that usefulness is never utilized due to how unreliable he is.
To begin with, Chiba only fights weaker opponents he knows he can defeat— the last page refers to how even if he came to her rescue, he only has the mental capacity to take the most savage, barbaric, extreme answer, much like how he ruthlessly crippled his attacker for life, and had almost no qualms killing him, nor would he feel remorse or guilt for doing it. Were either of those options to be applied to someone like a guildmaster’s son, who actually holds enough notoriety where other adventurers that might be strong enough to pummel him voluntarily choose not to intervene, it would be nothing but trouble.
Chiba, who only thinks about himself and his needs, is not qualified to skillfully diffuse this situation peacefully. Haru is merely lamenting that that useless otaku was the most reliable person she could... well, rely on, in this very specific situation. A lot of people could easily kill people that give them trouble. Imagine if Donald Trump just killed off any reporter he didn’t like, instead of accusing them of fake news and attacking them. Just because people are strong enough to kill people that trouble them, doesn’t make it any less socially acceptable.