Grandmasters were primarily unique from other classes. It wasn't because of their ability to use aura, it was the fact that they had no weapon restrictions, and this was below level 100, that is before the first ascension. Although, amongst the hidden classes to start with all of them were more or less equally unique.
There was a primary difference between classes selected in the beginning and classes either achieved or rewarded in the game. It was quite simple, classes either had hidden conditions or requirements or they were given as a reward. Of course, in some cases, they could be found in dungeons or perhaps even as drops from certain bosses. Amongst these classes, there was a special category that existed.
