User blog comment:Xilinoc/Ch. 686 - Death & Strawberry (End of Bleach reMIX)/@comment-5303512-20160819010913/@comment-1268838-20160819024551

Yhwach's motive goes all the way back to the start of the arc, with the explanation of the whole "Balancer" thing. It just really fell off for whatever reason. I don't think it was ever specifically stated that the Soul King created the Dangai, but I think that's what the whole thing was getting at.