The power of steel was one of the world's most diverse energy.
Based on the legends, the Initial Flame and Primordial Steel created the world of Mycroft. The source of all existence came from Primordial Steel.
Living beings which had more energy and larger body size would probably have the most 'steel' within their bodies. However, no matter how strong the 'steel' was, it was not something that could be easily controlled by the living. Mortal flesh could never ignite the potential of the power. Only by utilizing some special methods or facing a life and death situation would there be a certain probability which could awaken the power from within. All the warriors would have to go through a [Steel Revelation]. Only those who succeed could ascend from mortal to a Steel-tier combatant.