Second on that, Theinen.
I can just see it now: there is a lull in the war after everyone kicks Aizen&Co. out of fake Karukura, and they retreat to HM to plan their big attack on real KT in SS.
Isshin takes Ichigo aside somewhere and teaches him how to control his reatsu to prepare for Aizen's final attack. Isshin is obviously an expert on concentrating reatsu , based on his comments to Grand Fisher about his sword.
The training sessions will be funny as hell! I can't wait!
