I seriously think a lot of people need to go re-read this series(I might do the same when we finally get a new release date for the next volume). It was stated in every volume of the blade dance arc at least once that est's attribute of steel strengthens kamito's body making him more robust. It is stated many times that there are attributes besides the main ones of the elemental lords. For a more clear example, dragons. Go back and read about how Leonora is constantly using dragon magic(yes, dragon attribute magic) to enhance her body strength etc. Very clearly there is more out there than 6 elements.
|