Board Thread:Questions and Answers/@comment-25801533-20150531094407/@comment-25801533-20150603204213

Sternritter M wrote: Al things considered, it seems the family bond through Isshin is the reason why Ichigo looks so much like Kaien, since the reincarnation theory doesn't quite seem to match.

families in the soul society work very different than families in the world of the living. There is no way for the soul society families to reproduce (that I am aware of). If there is a resemblance it is because they were related in the world of the living. Ichigo may be the reincarnation of Kaien. Kaien, Kukaku, Ganju, and Isshin may all have been related and then joined the Shiba clan when they got to the Soul society, or their souls are always a part of the Shiba clan. Which would explain Ichigo's immense spiritual pressure considering his soul is from a "Noble family".