Then one day minato said to me that now that you have mastered the styles it is time for you to obtain the sword and the mask

 I knew about the sword but I did not understood about the mask.

 So I asked him what this is about mask.

 He said the mask allows you to take control over your body when you use soul eater

 And

 if you are able to make a contract with soul eater a body part of your body will change into steel.

I said why will one of my body part will change to steel?

 He said it will be the proof that soul eater has except you as his master.

 Then he said here is the legendary mask it will help you so be sure to wear it all the time.

 Then I wore it and went to the cave with the old man where the soul eater sleeps.