User blog comment:Xilinoc/Ch. 540 - The Sword Five/@comment-33447191-20130606193857/@comment-1351982-20130607203455

Also, (and please let's not make this into a shipping debate) the name Zangetsu Litterally means "moon cutter." When you think about the moon you imagine something that's white, mysterious, and dark. The old man doesn't remotely fit that description. Canonly, Zabimaru looks pretty much what you would expect him to be both Shikai and Bankai (I have suspicions that Tensa Zangetsu is an anomaly and it is not normal for zanpakuto spirits to have two forms), "Zangetsu." The entirety we have come to know as "Hollow Ichigo" fits the physical expectation more, and the importance and symbolism of the moon in the series entirty, especially Hueco Mundo, further makes the connection of what is very likely the real Zangetsu to hollows.