The Zero Divison!!
I think there's still some secrets that are left behing in the dust. Now, i personally believe that Isshin Kurosaki was once a former Zero Division Captain. Meaning way stronger than the Captain of The Zero Division.
When Isshin first, when back to his shinigami uniform, he battle gran-fisher. His spiritual Pressure was way above Ichigo's BigTime!!!Even Hirako notice the spiritual pressure.
Now the Question comes in mind, Why hasn't Isshin told Ichigo the TRUTH about Himself and Ichigo's birth!!!!!
Urahara-San Knows the TRUTH I believe but That's My question.
2) I believe one of the Zero Division Captains will Regconized Ichigo's spiritual Pressure, His Last Name, and will REVEAL SOME JUICY STUFF!!!!!!!!!!!!!!!!!