So I think the voice is Kurusu. But we also pretty much confirm that the zombies are a hivemind. But then, the question becomes What actually is Kurusu?
Because we've seen both other guys who became super human essentially turn into physical clones of how Kurusu looked. I bet Kurusu himself looked different before he became infected. We also see they all start taking off their clothes.
But recall that we saw the original Kurusu in his room talking to someone else in his head. I think that may be the true original Kurusu.
This of course raises the question of Hiromi's condition. She still has super strength but doesn't hear the voices or hallucinate anymore. Will it come back if she becomes emotional? If Oda dies (please no)?
This is the most interesting zombie virus I've ever seen, I think.