This Quirk allows Tetsutetsu to turn his body into steel.
Steel is tough enough to protect Tetsutetsu from bullets and tons of falling metal. 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.
Using his Quirk for too long will cause Tetsutetsu to suffer from iron fatigue, gradually weakening the steel's hardness. Steel also doesn't protect Tetsutetsu from all forms of damage, as poisonous gas can still be effective.
- 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.