Board Thread:Questions and Answers/@comment-25801533-20150531094407/@comment-25801533-20150601214032

Sternritter M wrote: I dunno with the manga, but in the anime, Ganju was just a little kid when Rukia brought Kaien's dead body back to his family.

I think it's safe to assume that Kaien died at least, I don't know, 40-50 years before the story began.

Rukia was adopted into the Kuchiki clan 40 years before the main story. It was after that that she joined squad 13. Some time after that she trained with Kaien long enough to achieve shikai. Then he was killed.

The Shiba clan used to be a Noble house before (for some unknown reason) Kaien's death. After he died the Shiba's were no longer called a Noble house but still had the blood line of nobles. So if Ichigo is the reincarnation he has blood from a noble house, and only once in several generations is a noble child gifted with massive amounts of spiritual pressure and is capable of achieving bankai at an early age (prodigy/genius).

Kaien also said he would always stand by Rukia even if he died (maybe as Ichigo).