User blog comment:Xilinoc/Ch. 540 - The Sword Five/@comment-5198194-20130606165615

Maybe Fake Zangetsu realized how dangerous and insane Ichigo's Zanpakuto Spirit (Hollow Ichigo) was, so he decided that he would be the Zanpakuto Spirit instead, so that Ichigo wouldn't get hurt. And I don't think he has Yhwach's memories (he doesn't act anything like Yhwach), I think he just looks like that because of the fact that that's where Quincy powers came from.