Originally Posted by
Amuramie
My understanding is this: the Sha are the fragmented remains of Y'shaarj. They are also described by Taran Zhu when you arrive in Pandaria as simply "negative energy." The Townlong questlines imply that the Sha seek "powerful hosts."
SO, I believe the way it works is that these fragments of Y'shaarj are attracted to and then exacerbate negative emotions. Shuhao must have been one crazy dude back in his early days and had all sorts of negative emotions floating around, attracting the Sha and allowing himself to become a host. It could be that his reign was tumultuous enough that he really did attract the "prime" Sha instead of the little pieces we see that corrupt minor NPCs in Pandaria. So to answer your question, they are Y'shaarj's remains, but had used Shuhao as their host.