The problem with the skill is, it could only be used by mages and doesnt allow for the use of magic while it is in effect aka completely usesless, best posible use would be to tank for a while (which can be pretty hard if you are a mage with no damage capabilities) . Thing is he can still use warrior/paladin/whatheverthefuckelse skill as long as it isnt magic. He is kind of abusing a bug since he can use all the skill of classes he maxed first to be able to use the class he currently has. In the game you could only use the magic/skills of his current class. Dunno if there was a problem with the traducction or the manga artist didnt wasnt to waste 3 pages explaining.