Like I've theorized way back in January, I believe the Juubi developed a form of consciousness over the eons, what Kurama described as the mindless/emotionless Juubi could be referring to its' primordial state, not the state when it attacked humanity during Rikudou's era.
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My hypothesis is that the Juubi developed a consciousness over the eons.
And that the Final Form of the Juubi is a conscious/talking Juubi
And this is the reason why it attacked humanity long ago:
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the Juubi attacked humanity as punishment for their sins (war,murder,destruction,etc.) and there's also that ominous statement by Rikudou to the Bijuus that "unlike when you were all inside me, you will be lead down to the right path"
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It seems to imply that the Juubi is within the sphere of morality, that it's not some mindless creature that attacked humanity for no reason, and if we think about it, the Juubi was present since the foundation of the world long before Rikudou was born, why didn't it destroy humanity way back then? why allow the pupa to become a fly so to speak.
Kishimoto's characters have always been purposive. Nothing happens without a reason. I seriously doubt that Juubi's attack on humanity was just something random.
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Madara thought that Kurama lacks sapience/consciousness, Hashirama and others thought of Kurama as merely a dangerous feral creature but it turns out he and the other Bijuus were not mindless animals, they had a reason to be antagonistic towards humanity, and since the whole (Juubi) is greater than the sum of its' parts, then why would the Juubi not have a consciousness or developed one?
Also, Hachibi said that Rikudou foresaw the full revival of the Juubi would signal the end of the world.
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Since Rikudou probably had the gift of foresight, then why did he say that? why did he not foresaw the casting of Mugen Tsukuyomi? Rikudou's prophecy seems to imply the world's destruction, not the eternal slumber in the Mugen Tsukuyomi. Unless he foresaw it wouldn't be successful, that the Juubi will break free from Madara and Obito's control.
This is a common literary plot device known as "misunderstood creatures" creatures who seem to be evil, or not necessarily evil but harmful, but the truth is they're not, we have just seen the human-side of the Bijuus, is it not possible to see the "human-side" of the Juubi? perhaps it merely attacked humans because of their wanton disregard for life, perhaps this primordial creature had enough of humanity's destructive ways and decided to once and for all eradicate humanity.
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There is also the matter of the absolute finality and closure to the series, even if Naruto becomes the Juubi's Jinchuuriki like Rikudou, the cycle will continue, Naruto will eventually die and the Juubi will be set loose. So to me the only closure I can see Kishimoto doing is that the Juubi will place its' faith in Naruto much like what the Bijuus did, but for that to happen, the Juubi must be conscious in the first place.
Naruto will convince the Juubi to believe in humanity and will leave them in peace forever.
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UPDATE
Remember this panel:
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It says Speak, See and Hear no evil.
Kishimoto is presenting the element of irony
Speak no evil and yet it has a mouth
See no evil and yet it has an eye
Hear no evil and yet it has an ear
We're probably going to see a conscious Juubi like the Bijuus when it's fully transformed.
