User blog comment:Xilinoc/Ch. 630 - The Twinned Twilight/@comment-24726378-20150611162918/@comment-24153155-20150611223704

To me, it kinda seems a secondary thing. In chapter 565, it is explained that Yhwach "played" with those that were "lacking" something, by giving them exactly that they were lacking (you can also read this under Yhwach on this wiki). However, what seems to be apparent is that all of the Sternritter -of which we have seen their pasts- were mentally unstable. Perhaps they were rather easily brainwashed by Yhwach?