User blog comment:Xilinoc/Ch. 553 - Frozen Cross/@comment-29183117-20131016194159/@comment-11051098-20131016225945

"The Iron" could mean that he's very durable, like you proposed, perhaps more than what only his Blut makes him. But I hope Kubo doesn't screw this up and kills off Cang Du and BG9 that easily.