User blog comment:Xilinoc/Everything but the Rain op. 10 - "Prinz von Licht"/@comment-4957813-20130515162549/@comment-6904925-20130515165835

Because Yhwach "picked" the Quincies who he thought were "impure", it didn't just apply to mixed Quincies it also implied to pure blood as well, as he stole the powers of Masaki who was a pure blood Quincy.