I'm beginning to see the bigger picture, now, and how the mogu relate to the Titans. But every answer brings with it more questions!
The only way to put this puzzle together is to find every scrap of Titan information we can scavenge from the Thunder King's palace. Destroy the Thunder King and his minions and collect as many Titan runestones as you can find!
Thanks to your work, <name>, we've reconstructed an ancient narrative. The mogu were once creatures of stone, enacting the will of the Titans. But then their master fell silent, and they succumbed to the curse of the flesh. Eventually Lei Shen came along, imprisoned the keeper Ra, and took his power. Ah, what an empire he built!