This whole time I have been reading and watching Bleach I have wondered exactly how much these two have in common. What brought this issue into focus started when Urahara forced Ichigo to return to being a Shinigami. I thought it was a bit significant that he put Ichigo into a position where he was in the process of turning into a hollow before being guided to his zanpakuto by old man Zangetsu. I wondered why finding his zanpakuto was so important.
Later when fighting (and loosing to) Kenpachi (old man) Zangetsu brought him back to his world to test his resolve and decide if he was worthy of wielding him and forcing him to confront the Hollow inside him. It wasn't so much the struggle against the hollow that held so much significance to my thinking it was the conversation between the old man and the Hollow after Ichigo returned to continue his fight with Kenpachi.
These questions only became more focused when the Hollow took over during Ichigo's fight with Byakuya. Not to mention Byakuya's willingness to overlook and not question the transformation. That just made me wonder how much he understood what actually happened with Ichigo. It was also the point where I began to question the significance of the bead like piece Byakuya wears in his hair.
My questions began to take the form of suspicions as to the meanings of these links as the latest (anime) arc began to unfold, namely with the contact of the Vizard. When Ichigo sought out the Vizard and was forced to again confront his inner Hollow, it was the Hollow's declaration that he was Zangetsu that really got the wheels turning. The turning became a blur of mental motion after the explanation from the Arrancar that the release of their zanpakuto unseal the bulk of their powers as well as their completed forms.
So where am I going with this, right?
Ok, here is my hypothesis. I don't think there is much difference between Shinigami, Arrancar, or Vizard. I think it is all in how they channel and seal the power of the Hollow inside each of them. Shinigami compress and seal their inner Hollows within their zanpakto, yet never really capitalize on the power that they have sealed. Mostly because of a lack of understanding of where their zanpakto draw their power from.
Arrancar have a better understanding, but still fall short of the potential of said power. However this could probably be due to their having started out as Hollows in the first place. Vizard seem to understand that by drawing on the power of their inner Hollow increases their strength and ability significantly. However I haven't seen them draw from the power of their zanpakto like Ichigo did during his fight with Kenpachi.
It was Ichigo's inner Hollows closing statement in episode 125 that if Ichigo really wanted to control his power, not to die before he showed up again that really got me thinking. It brought me back to the 3 stages of Byakuya's bankai. How come, I wondered no other Shinigami had more that one stage of their bankai? Is that thing Byakuya wears in his hair actually some remnant of a hollows mask? Is he actually (however unknowingly) also a Vizard?
Anyways this is the direction my thoughts are going. I would be curious to see what the rest of you can add to this thought line. So I guess we'll see now that I have raised this idea up the flag pole, who salutes it and who shoots at it.