I think he doesn't truly want to kill humans. I think he's just trying to make Rai fight him seriously. Like he said in the latest chapter, he could rampage in say another country and Rai would be none the wiser. I kinda get the feeling that what he really wants is to die by Rai's hand.
Why he wants to die by rai's hand? Why he wants to fight rai? Did i missed something?
It's a guy thing and a plot line that I've seen in other manga. I'm not sure it's what Muzaka really wants, but it does explain why he keeps provoking Rai. In the latest chapter Muzaka says that there was no time for him or Rai. He knows from that Rai is running low on power/life force from their battle against Maduke. However, his comment that neither of them have much time left makes me think that he's also close to death. Slowly wasting away in his deathbed is definitely not how a warrior like Muzaka would want to go out though. Most of the time, warriors like him prefer to die on the battlefield. However, the only people who might be strong enough to kill him are Raskrea and Rai. He and Rai are old friends and they never did finish their fight centuries ago. So, it makes sense to me that what he really wants is to die by Raizel's hand. (This theory is mostly based on my own intuition though.) ╮(￣▽￣)╭
If you want to start killing human,why don't you start with your companion "doctor"? Lol... i bet you wouldn't do that! Grown up please.