Quote Originally Posted by Buffalobiian
The term "sway of magic" itself sounds rather awkward, though if you see it as just a modified version for "corruption of power" or something, I can live with it.

Anyway, it totally threw me off when Justin was revealed to be a bad guy. The anime sure changed things huh? I guess along with Marie's hammer form, they came up with Justin's Law-Abiding-Silver-Gun too. <- which was pretty awesome in its own right.
The term may be just a mistranslation by the subbing team, just like Ryu said

As for Justin's finishing move, it came from the manga

http://www.onemanga.com/Soul_Eater/26/30-31/