Tite Kubo did not author that arc, it is a filler arc for the animie only and has no connection with the story that Kubo creates.
Everything of course is up for speculation but some things are in front of us.
- True I've just managed to reason out myself any flaws in storyline between filler and non-filler. I don't like flaws so I deal with them as I see them or when presented with new information. I would like to think that Kubo assisted with fillers whether it be via advice or briefly looking through it's story. Even if he didn't an example of working out a potential plot hole would be Muramasa using his ability to call out Ichigo's Asauchi when they first met. When Muramasa called out to his soul, two beings appeared before him. One said, Hi I'm Zangetsu and the other said screw you and remained within Ichigo, granted this other (Whitey) gained control of Ichigo's body and went berzerk. Muramasa's ability succeeded in bringing out Whitey but failed to make him turn on Ichigo, whilst successfully bringing out the Ol' Man who at the time is the container for Ichigo's unsealed Zanpakutou which could explain why he was called out. There's maybe one or two other reasons for why Ol' Man Zangetsu was able to appear before Ichigo and Muramasa but I don't plan on mentioning them because one isn't all that solid (like walking on glass) and I currently can't remember the other one.
- One other thing I have considered is a potential compatibility between Shinigami power and Quincy power but I don't put too much thought into it.
First we can draw a connection between chapter 541s Old-Man and chapter 411s young "Tensa Zangetus", or Young-Man(?). While Ichgio first visited his innerworld in Bankai form, he faced off against Young-Man. Young-Man stated to Ichigo that what he wanted to protect was Ichigo himself but was never explained. Old-Man in 541 explained to Ichigo why he wanted to protect him. Thus it's easy to conclude that Old-Man and Young-Man are the same.
-I agree with you as far as what they wish to protect but for me that alone isn't enough to make me think of them as the same person. In addition to that, if the Ol' Man represents Ichigo's quincy powers then how could he change form upon the release of his Bankai. In the manga I remember the young man stating that he would lose all of his shinigami powers upon using the Final Getsuga. I believe that the young man was the manifestation of his Shinigami powers and was destroyed with the Final Getsuga. Ichigo did not re-enter shinigami form until the combined power of soul society restored his shinigami powers after he had completely lost it. When Ichigo uses Mugetsu the Young Man says "Farewell, Ichigo". If he were Ol' Man Zangetsu I don't think he would have said that let alone lie to Ichigo a second time. The Ol' Man doesn't have to worry about vanishing upon the use of Final Getsuga. The Ol' Man is the manifestation of his quincy powers, of course he'll be fine. I could be wrong but that's how I see it.
- A little side note: We may see the return of the Young Man with the release of Ichigo's un-sealed Zangetsu, granted he may appear to Ichigo in a "changed" form.
Both the Young Man and the Ol' Man care for Ichigo and appear to look out for his best interests, with the release of this latest chapter we realize at one point that the manifestation of his quincy powers (ol' man) didn't want him to become a shinigami because he knew Juha Bach (current) was going to try to kill him if he did. However, now that he has become a shinigami he is pushing for Ichigo to reach his max potential and is "willing to step back" and get out of the way of Ichigo becoming stronger. If you think of the Young Man representing Ichigo's shinigami powers you can also see why he was upset when Ichigo learned the Final Getsuga, he wanted to be there to protect Ichigo. Again, the Final Getsuga destroyed his shinigami powers (Young Man) which were restored afterwards with the help of Soul Society.
Things that cause much speculation right now with Ichgio is:
1: Why did Old/Young-Man fuse with Hichigo?
2: Since we now know that Ichgio is being revealed his true Zanpakto, does this mean he never learned Bankia?
In reference to point number two: Shirosaki has been revealed as the source of Ichigos true Shiginami powers. Shirosaki, aka Hichgio, has never revealed his name yet also stated that he IS Zangetsu. However, it was Hichgio that taught Ichgio about Getsuga Tensho, the same Shiginami ability Ichigo's father uses. And, everytime Ichgio went Bankai prior to vizard training, Hichgio became closer and closer to Ichigo.
It's safe to say as of right now that Ichgio's Shiginami powers derive from Hichigo: A collection of Shiginami souls fused together and holowfied by Aizen, which have been absorbed by the mother and passed down to the son as a Shiginami entity thanks to the fathers constraint.
- Yes, Whitey fused with Ichigo's Shinigami powers and via the release of recent chapters we know that he is also Ichigo's Zanpakutou "Zangetsu". However, despite the fact that he fused with his Shinigami powers, Whitey is still a separate part of Ichigo's shinigami power (his hollow powers). It makes sense that his hollow powers manifested itself apart from it's shinigami half up until the point where they had to rejoin to teach Ichigo the Final Getsuga.
- What I'm saying is that Whitey and the Young Man are the same being/Asauchi but at the same time they are separate, they are linked but at the same time can appear apart from each other. If the Young Man really is the manifestation of the shinigami half then it is completely possible for him to release a Getsuga Tenshou whilst appearing apart from Whitey. I believe that prior to Final Getsuga Tenshou, the Young Man and Whitey were both Ichigo's Asauchi known as Zangetsu but more unique than any other Asauchi to date. Both are the same Asauchi but at the same time they can be apart from another each representing one part of Ichigo's power: Shinigami and Hollow.
Sorry for all the reading ,-,
