Edit, Ichigo as I am stated earlier IMO Ichigo will unleash his Zanpakutou without Zero Squad dudes Asauchi. He says not one person has achieved this feat. I never really thought of the fact that Zaraki actually stole another's katana. Interesting I guess if he would of bonded with his sword early on he wouldn't be in this predicament. Also assuming after a shinigami's death the Asauchi would need time before it bonded with another.
Also as I figured but I didn't catch Isshin was his head of the house.
This is before the Rukia/Kaien confrontation correct or wrong?
Another assumption (obvious) here is that Aizen is behind the hollow who they modified (mock arrancar) to attack Narukishi town. Possibly this is where Isshin confronts the mock arrancar and possibly reports back. Understands that with his own power it isn't enough?? Trains his zanpakutou to it's final stages??? Meets Arrancar again, defeated in Kakaraku town with Masaki saving face???
EDIT#2: NARUKISHI CITY.... name sounds quite familiar