User blog comment:Xilinoc/Ch. 552 - The Fundamental Virulence/@comment-1351982-20131008134737/@comment-1351982-20131008140509

Also by "iron" Kubo is referring to someone who is cold hearted and its possibly a reference to 1992 film Ironheart http://en.wikipedia.org/wiki/Ironheart and Iron Heart is also the name of a Japanese clothing company that focuses a lot on American workwear and Motorcycle clothing.