It's only been 12 chapters, just have some patience. From chapter 1, he's never been a person to act out on his own behalf, but when it's his daughter who's about to get stabbed, or Akama who's getting attacked, or Nero who's about to get thrown on the ground like a birthday cake, he takes action. He'll probably kill the end human next chapter as an act of defense for another.
And if not now, there's at least the promise that he'll eventually be capable of fighting back given by the title art.