User blog comment:Lia Schiffer/397: Edge of The Silence/@comment-1769234-20100329025210

This is my theory that 20 years before the beginning of the story line Isshin was the captain of squad 10 then got promote to the royal guard (Zero Squad) though he knew of Aizen's plans and which to join forces with Urahara though while looking for him he found a women Ichigo's mother and fell in love. Though as a Shinigami he could not be with her lets say that so to be with her Urahara made a gigai that would fuse with him making his spirit form into a physical form thus making it possible to fall in love with her and having children with high spirit energy though made him lose his power until he left the physical form.

As for Aizen all I can think is since his spirit energy rivals Head Captain Yamamoto's and having a Zanpakuto that can control the five senses he believes he should be the Soul King an my second theory is since the Soul King gave the ruling of everyday events in the Soul Society he believes that the King viewed as a God should be killed thus making him one though all these are theory not fact.