User blog comment:Xilinoc/Ch. 619 - The Betrayer/@comment-1248963-20150313015601/@comment-5398287-20150313084559

At the very least Yhwach's claim is somewhat justified by having a piece of his soul within Ichigo from birth, with said piece of soul having caused at least one of the events he mentioned (Ichigo losing his powers against Aizen). Aizen never had anything like that, though he clearly wanted to get inside that booty if the little "I can touch your heart" moment in Fake Karakura Town is anything to go by.