Board Thread:Questions and Answers/@comment-18812574-20150614041041/@comment-1493741-20150614172013

I don't believe the latter quote is referring to it being "Quincy-only", rather that its clear the one in control of it is no longer the Soul King. The problems creating footholds were present even before Yhwach took control for example, and I've thus far been taking it as a matter of density. The concentration is just so dense that they can't create the footholds they would normally, hence why the Royal Guard use such odd means of crossing the cities and why Ichigo fell threw the floor of the palace instead of just standing on air.

The idea that I generally work along is that Reishi is neutral, but can be "converted" to serve a purpose. Each person's body is made up of Reishi aligned to them, but Quincy can use Sklaverei to dominate that Reishi, taking it for themselves and absorbing traits of the person they stole it from and so on.