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. Since his body is made of metal, it is safe to assume he is vulnerable to electricity, making him a bad match up for Denki's Electrification Quirk. It is unknown if he is magnetic or if his body can be pierced by stronger metals.
- 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.