The explanation that Analei had given him couldn't have been simpler.
Someone with their Aether bound to their Will. Or, in other words…
Willborne Intelligence.
When Sylas saw this, he realized that he had no such thing. Was he really a Cryst Emperor? Or did he just have a convenient Class that allowed him to cosplay as one?
Maybe to say that he was cosplaying as a Cryst Emperor was correct, because his reliance on his Aether could be said to be quite pitiful. His use of his Aether went as far as activating his Skills and no further.
