(Note: This post excludes all fights after the timeskip, as I have not watched them. This post also has spoilers.)
The ultimate fight, in most cases, is both the greatest and the last. However in this case Ichigo’s battle with Aisen was not really his last battle, and in my opinion it was certainly not his greatest! It was the battle between Tensa Zangetsu and Aisen. Due to the fact that the final getsuga tenchou was Ichigo turning into another person, a power that was very suddenly introduced as the final battle was fast encroaching, this was not truly his battle. This was a battle which was solved with a near miraculous stroke of luck, a Deus ex Machina.
Ichigo admits himself that he is never a match for Tensa Zangetsu and that there is too great a difference between their powers. In the end he gains the final getsuga tenchou by submitting to Tensa Zangetsu in battle. Thus he never really won this final battle, not even indirectly.
Instead I believe that his battle with Ulquiorra was his ultimate fight. He may not have fought him directly after changing into his fully hollowfied state, but his co-existence with the hollow inside of him was set up from the very beginning of this show. It was explained that he constantly had to fight against this hollow to remain in control of his own body, and that he could both borrow its powers and be taken over by it during fights. Every time this happens he has to battle against it to regain control. So when Ichigo fully hollowfies and defeats Ulquiorra, he then has to defeat the hollow and so he still fought this battle. It was simply an indirect victory.
I found Ichigo’s fight with Ulquiorra to be my favourite out of the many battles in Bleach. It was the most entertaining, and the most meaningful moment of the show. I also think that it would have made for a strong and poignant ending.
Please comment to let me know your thoughts.