Board Thread:General Discussion/@comment-24815992-20140522154132/@comment-11051098-20140523200922

Seeing as Isshin and Ichigo have similar names and a fellow attack in their Zanpakutôs, this might be a "rule" for families in the SS as well. For example, we know that Tetsuzaemon Iba is the son of the former 3rd Division lieutenant Chikane Iba, they might have had similar Zanpakutô names too for all we know.

Or maybe this just goes for close family Captain level Shimigami? Who knows. Or maybe Kubo just made it like this for some other reason.