User blog comment:Xilinoc/Ch. 540 - The Sword Five/@comment-10478852-20130605202237

It seems like I understood some things in a different way compared to you guys. Here's my version :

It has been clear in the manga that Ichigo's powers were manifested by only one "spirit" in his inner world (the Hollowified Tensa Zangetsu), so it had always been like that since the beginning. The different entities we saw in the manga, Hichigo and Zangetsu, are representations of Ichigo's different powers.

At the very beginning, before he met Rukia, Ichigo had Shinigami powers from his father, not represented by a spirit in Ichigo's inner world, and Quincy powers from his mother, represented by Zangetsu the imposter. The real Zangetsu hasn't shown himself in the manga. This imposter is just a manifestation of Ichigo's Quincy powers, and is NOT Yhwach himself, because Ichigo has Yhwach blood in himself. He also got a hollowification from his mother, but it wasn't activated since Ichigo's father was still bonded to it.

Since Ichigo's powers are manifested in only one person in his inner world, the imposter Zangetsu was the main representation of Ichigo's powers, having both Ichigo's Shinigami and Quincy powers. And since Yhwach said Ichigo's Quincy powers were dormant, the imposter Zangetsu didn't know himself he was the representation of Ichigo's Quincy powers and ended just using the Shinigami powers, so he only knew his Shinigami part and ended calling himself Zangetsu.

When Ichigo's chain began to be destroyed, the Hollowification inherited from his mother was activated, thus ending the bond with his father. Like it was said in the recent chapter, the hollow born from this process, fused with Ichigo's Shinigami powers, fused with Zangetsu, and became Hichigo, but the imposter was still the dominant spirit in Ichigo's inner world. When all his powers were fused in one single being, Ichigo's powers were manifested by the imposter Zangetsu.

Also, since only one spirit represents all of Ichigo's powers, it is affected by all the different powers of Ichigo. That's why the imposter got younger when Ichigo entered his inner world while in Bankai state.