I think that the most interesting part about all this is that Madara
WAS expecting for Nagato to bring him back. (I added a little more detail to that part of my post after re-reading it). Because Tobi also confirms that Nagato's Rinne Tensei was supposed to be used for him, this means that there's a connection where their planning falls along the same path, or (to some degree) they both consider themselves Madara.
What's interesting is that I think that Muu's splitting Jutsu is being used right now explicitly to explain the duality of this relationship. While it doesn't say whether or not Tobi is a Zetsu with Madara's will transferred into it, or just a carefully perfected clone, it's a bit of a moot point now, because it brings up the duplication paradox. To explain this really easily, we'll use the following comparison:
Key:
• Madara = Sealed Muu
(A)
• Tobi = Split Muu
(B)
Muu splits himself into "A" & "B" who don't share each other's memories.
"A" dies & is sealed away.
"B" continues making plans and executing strategies for 5 years.
"A" is unsealed and brought back to life.
Now: Are "A" & "B" the same person since they no longer share memories, and may have developed different viewpoints?
Given the relationship explained above, here's my theory as to what happened:
After his battle with the Shodaime Madara was greviously wounded, a shadow of his former self, and unable to continue surviving to fulfil his ambitions. Working with Black Zetsu (who may have been recording the battle, like he did with Naruto & Sasuke), they managed to create stable bodies from the Senju DNA/biomatter that he obtained from the Shodaime Hokage. Since these bodies are able to absorb an individual's Chakra and mimic them, Madara created a copy of himself. Since he can directly interact with this copy, unlike the Zetsu that we're seeing in the war, it could be an exact match. In order to differentiate between themselves and for Zetsu to be able to tell them apart, Madara kept his hair long, while Tobi had his hair short. This would leave Madara & Zetsu as the individuals who know the entire truth.
Since he couldn't risk dying himself, and Tobi's body is naturally more versatile, Madara used Tobi in order to execute the various tasks that he wanted to accomplish. At this early stage, Tobi isn't any more than just an external body for Madara's ambitions, and doesn't identify himself as Madara when he meets Minato, because at this point he's still just a copy. In truth, because of his DNA, Tobi is much more than that. He's the embodyment of 2 of the 6 paths, whereas Madara himself is just 1 of the 6. In working to fulfil these plans, Madara begins manipulating things from the shadows and forming Akatsuki.
At some point, we know that Madara dies. I'm assuming it's at this point that Tobi comes more into the spotlight, and eventually completely assumes the mantle of Madara, since in the absence an the original, the clone can become the genuine entity. His line,
"The Sharingan's true power... my power... Ushiha Madara's power...." very much reflects the idea that HE is now Madara, and he truly becomes the single vessel of all of Madara's ambitions and dreams, rather than just a duplicate. Over time, he moves into a more prominent role in Akatsuki, gradually becoming more possessive over his identity.
At this point in the War, Tobi's now embodies 3 of the 6 paths, and is fulfilling what I'm assuming is Madara's original dream/ambition in ways that Madara never could. I have to wonder if at this point, because of everything that he's done, even if as a copy, if Tobi still sees himself as more genuine than the original- a more true version of Madara than the one who died. This connects a bunch of themes that have been present since really early on in Naruto, like the idea of becoming a tool and fully becoming the embodyment of someone else's ambitions to the degree that they then entirely become your own.
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