Zaen will be able to resist that due to insanity, but I can see him not caring about death. After all, he gets killed, he's reborn. The way he works with pain is that he'll feel it intensley when it happens, but once the pain goes away, he forgets about it and doesn't care a single bit, so if he's reborn in fire, he'll just keep coming back and kiling the others, and since they feel pain differently, it'll be a victory for him! And most people don't like getting stabbed with a knife