User blog comment:IamJakuhoRaikoben/Sorcerer Magazine, Issue 17: May 2013/@comment-4829046-20130605090234/@comment-4829046-20130606024859

Haven't you read RAVE? C'mon! Mashima had this concept since long ago.

Also in my way of thinking(ironically) there are only two legendary swords; One forged of darkness and one forged of justice. All the swords great are stemmed from just these two swords. And the ones of justice can only be wielded by one of pure heart. The one of Darkness is a stark contrast as it lets anyone wield it, but corrupts the wielder instantly, filling them with madness and making them into tyrants. Only those that have conquered insanity can wield it without consequence.

This concept is a basic concept followed by most media and myself.