There’s no denying that Madara’s as overpowered as they come in the Naruto universe (right up there with Naruto himself), but while it’s easy to jest about how he’s dropping massive meteors on the Earth with Chibaku Tensei, I don’t particularly mind because the story’s been building up to this big revelation for some time now. This is unquestionably one of the most earth-shattering moments of the entire series, as it establishes the missing link between the Sharingan and the Rinnegan. i.e. The latter is a direct derivative of the former and not simply a unique doujutsu possessed by Rikudou Sennin.
Speculation from chapter 510:
At this point, it’s hard to say if transplanting a Sharingan into a Senju descendant along with some DNA manipulation is enough for it to evolve into a Rinnegan, but that’s definitely one possibility on how Madara “gave” Nagato his eyes.
(Reminder: Nagato’s a descendant of the Uzumaki clan.)
I threw out the idea a while back about how the Rinnegan could possibly be an evolved form of the Sharingan if it’s crossed with Senju DNA — back when “Tobi” said he gave Nagato his Rinnegan — and it’s really starting to look like that’s the case. There’s precedence for it as well, given that the Uchihas supposedly inherited Rikudou Sennin’s eyes and the Senjus his strength, so the secret that Kabuto’s been alluding to could very well be the mixing of the two bloodlines to recreate the ultimate ninja. It would be similar to Underworld’s take on vampires and werewolves, which also had the two races engaged in a war against one another for as long as everyone could remember.
Assuming that’s the case, I’m left wondering if there’s a catch to it. For all we know, it could’ve been perceived as taboo to mix the bloodlines (again like Underworld), so this may have even been the root cause of their fight for control over both clans. The biggest question lies with Madara himself, who mentioned here that he only awakened his Rinnegan shortly before he died. Part of me gets the feeling that the awakening may have been what killed him — going back to the idea why it’s taboo — and that he was banking on Nagato to develop his own Rinnegan from “Tobi” (whom I’m still learning towards is Izuna) to later revive him using Rinne Tensei — the deus ex machina-like technique that Nagato used to revive Kakashi and all of Konoha’s other victims. This would explain Madara’s surprise last chapter that he was revived with Edo Tensei instead of Rinne Tensei — something that was incorrectly translated in the scanlation that 99% of English readers probably rely on (page 2). 「…穢土転生だと…！？ 輪廻転生ではないのか…！？」
At the moment, I really like the proposition that Madara and Izuna may have planned this from the very beginning to usurp power from the Senju, considering the ambitiousness that not only spans multiple generations but also death itself. As a natural counter to that, I can already picture Naruto and Sasuke reuniting the Senju and Uchiha bloodlines in a way that corrects their ancestors’ mistakes. If at some point down the road, hundreds of chapters from now, Sasuke tells Sakura to transplant his eyes into Naruto to awaken the Rinnegan and stop Kabuto/Madara, just remember that you heard it here first. 😛