I think that was justified too, especially because he had never met him before. His bio father made the ultimate sacrifice to basically save the world and all the nobles and their children from certain destruction. But they’re awful people, at least from Niro’s perspective. The people who enslaved him, abused him, killed his adopted mother, and ridiculed him endlessly were saved in exchange for his father.
As someone who has had their father not be in their lives for whatever reason even tho we meet sometimes, I can say with full confidence, that I would probably care more about the person who raised me and taught me about life that someone who wasn’t there. When his father dies, I don’t remember Niro going on a streak of beating up people. It’s like he doesn’t care about the consequences, even if those involve her sisters

Niro is a shiet protagonist