User blog comment:Xilinoc/Top 10 Characters of the Blood War Arc/@comment-24769684-20161029022136/@comment-29359011-20161107081654

Uryū can designate any two targets and completely reverse anything that has already occurred between the two of them.

Uryu probably reversed his own possible future with Yhwach causing Yhwach unable to see Uryu's action the moment he shot the arrow.