First set of updates will jump around a lot. To establish a timeline of sorts (until Canon rolls around). Keep an eye out on the chapter titles for the year they're set in. Konoha's founding occurred in year 0.
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He'd always firmly believed his mother to be the world's greatest danger. The princess's presence over the horizon the one thing that rose above all else. That held every last spot of chakra he had in reserve. Unable to risk wasting it elsewhere.
Even as watched the world he loved rust. As he watched it's people mutate his teachings. As he witnessed his family's sealing. As he walked battleground after battleground searching for peace, alone and drifting.
He'd given up everything to make sure the world didn't wither away under the shadow of his mother, and here he was, witness to what he'd left in his wake.
War after war, after war. With every generation eclipsing the previous in power and destruction.
In ideology and determination.
In recklessness and stupidity.
He wasn't sure when everything had started going wrong. When that first spark of fire ignited in ignorant hands.
He'd left behind a peaceful growing world, his only worry the inevitable return of his mother. And within decades, the warring era of what would come to be Shinobi history had begun.
Century after century he'd kept a silent vigil. He'd seen powers from every spectre show themselves. And with every century's turn, he'd seen the escalating skills and abilities of the average person keep a steady rise, never truly diminishing.
The martial-oriented state had put the world's focus towards power. And power alone.
And when his children's direct descendants had joined the fray, their temporary peace at last shattered, or rather forgotten. The steady line had turned into a curve. His direct lines abilities unparalleled in adapting and learning.
In a matter of decades, the Uchiha and Senju clans had quickly eclipsed near everything else the world had to offer. Learning and mastery jutsu the general populous boggled at. Abilities the likes of which the others couldn't fathom.
The Senju for their life-force and prodigious talents, their mastery of senjutsu unequal. And the Uchiha for their prodigious talents and bloodline and given half the abilities engrained into every one of them, albiet with conditions, not much needed saying there.
When the Uzumaki had finally showed themselves with their frankly inhumane sealing power and wonderful personalities. He had, admittedly, almost cried out in joy.
Truly, if every clan followed them, the world would be a much better, albiet short-lived, place.
Though not as war-hungry as the rest, the Uzumaki had their own... Quirks. The land of whirlpools certainly only received it's whirlpools moments after an Uzumaki figured out he could manipulate water.
Of course, even with the number of clans escalating rapidly, the varied powers of Ninjutsu expanded. Hagoromo knew that until his sons were reincarnated, the worst, in terms of growth, was yet to come.
And come it did, in the form of Hashirama Senju and Madara Uchiha. And while the second had played well into his role, the first had utterly shocked him, just as his eldest did those centuries past.
Hashirama Senju had vied for peace. And for a small moment, Hagoromo dared hope it would last. His dream finally coming to fruition. The world finally ready to take it's first step towards change for the better.
And given the sheer raw talent possessed by both of the reincarnations, he had for a moment, believed he'd seen the pinnacle of what chakra, and the destruction it left, could reach.
And then, Danzo Shimura joined the fray.
And for the first time in his long-lived life, the shadow over the horizon changed.
...