This Quirk allows Tetsutetsu to turn his body into steel. It can be used as both the strongest defense and the strongest attack.
Using his Quirk for too long will cause Tetsutetsu to suffer from iron fatigue, gradually weakening the steel's hardness. Tetsutetsu has said that he will gain longer and stronger use of his Quirk depending on the level of iron in his diet. It is unknown if this refers to foods that had iron in them, or literal metal.
- This Quirk is very similar to Hardening, but turns the user's body into steel instead of just hardening the skin. The two also appear to be roughly equal in terms of power and effectiveness.