I explained a bit more on it,
The Nanomachines introduce a chemical known as Doxihydratorica, which when applied to the underlying skin allows the skin to harden organically, and naturally temporarily. While its in this hardened like state it is more akin to a titanium weave then Iron, allowing for exceptional defense, while not hindering the movement of the host. To keep this going, however, they need a constant dose, but to keep it from being to dangerous or permanent the Nano-machines will die out themselves in a matter of 3 hours.
However, as said it is not as defense savvy as say the PA or Mecha, so fighting against things like Mecha or PA is a rather dangerous endevor and must be approached carefully.