[Kazu-kun]

Originally Posted by aohige

Boy, and here I thought "hate" would be considered negative by Rukh.

Spoiler for spoilers 160:

I don't think he's acting on hate. He doesn't seem to care about power either, or changing his fate. Rather, I think he truly thinks this is the only way to save the world. No, not the only way, but the right way.

Basically he believes he's enacting fate, and that's way his Rukh doesn't turn black. The Rukh turns black when you curse your fate.