User blog comment:TheBody84/Ichigos father being the former Kenpachi/@comment-1655159-20091025071116

@ .wicked. thought the same :)

But if he's former 10th squad captain, shouldnt guys like Kyoraku and Ukitake and Unohana recognize Ichigos reiatsu being familiar with Isshins, as they are the oldest captains (not counting gramps in as he hasnt spent that much time with Ichigo as Shunsui and Ukitake) and if Isshin has been a captain before leaving soul society, they should know him?

So, what I think is that he's from the 0-squad, but was banished (or something alike) because he got somehow involved with Aizen or Kisuke.