Even though he knows that he's not wrong, something about the look Kai gives him kind of wants to make him fold just like that. But it just doesn't make sense. "I've seen spirits work with iron," he says, brow crinkled and really not sure what else this person could be talking about, "...Is it just that iron hurts you?" Specific to spirit weakness, he could maybe see. Even if he has no idea what kind of domain one would have to have to possess such a weakness.