User blog comment:God of nothing/Shiba clan logic/@comment-7658432-20130501001044

While Kaien may be a Lieutenant, you must not forget that he is genius as well as young. He has yet to achieve Captaincy but was killed early.

Maybe the Shibas really fell after the death of Kaien because Kaien is a prodigy, has way more potential than Hitsugaya but less than Aizen's potential. I forgot where I read that even Kaien's potential is greater than of Gin's (who was also considered a genius). So after he died, they really lost much of their power. Of course, Isshin's desertion surely hurt the clan. Their head, a Captain, just left (whether he left a message pertaining to his whereabouts or not) with almost no readily available replacement.

Hey, that's also my first thought when Kukaku mentioned "uncle". For me it read out as "Isshin". Glad someone viewed it the same way I did.