Board Thread:Questions and Answers/@comment-28540184-20160712115431/@comment-37873147-20190210000430

Consuming Yhwach's blood is his way of controlling the sternritters, as it prevents them from developing powers on their own or using Letzt Stil which allows further independence from the quincy king and tightens the bonds of trust with other quincy, which are needed to return the lost power. Just like the Lloyd twins where developing "The Yourself" from birth, Uryu was on his way of developing the anti-thesis because his grandfather groomed him to be independent of the quincy king, which caused Yhwach to hesitate to take his powers as a child; if he survived the auswahlen he would eventually be able to use his powers to reverse its effect (which he did anyway with the soul silver arrow Ryuken created). By giving him the schrift he made sure Uryu would come rely on the quincy king's power instead developing it on his own, which eventually would make his Auswahlen deadly on Uryu just like it was with Robert, Gerard and Haschwalth all of whom relied exclusively on their shrift to fight.