Note: If Daneel Rush is reading this, please forgive me for twisting the idea behind your Fuuton: Sasayaku Kaze no Jutsu into the Kaze no Teisei in the next chapter. I'd be willing to modify it if you wish.
Note 2: As per the rules of this site, I try to avoid "self-insertions" as much as possible. Therefore, I will avoid responding to reviews within the story as much as possible, though I'll try to always credit the original authors for their ideas, and I'll also always try to warn the users when I'm using ideas without the author's explicit permission. There are some issues that I do address in the A/N section, though those are rare. Rest assured, though, that I will respond to reviews if you leave questions or issues there.
Note 3: This story no longer follows canon as of chapter 499 (manga). I may use some later elements if they fit the storyline, but don't expect anything true in canon after chapter 499 to have any significance here.
(Just in case it's needed) Disclaimer: I don't own Naruto or any of the characters in there. This story was written for my own pleasure; I gain no monetary remuneration from it.
In a time long forgotten, in a time when each man had to fend for himself and could not trust enough to stand any other's presence, demons freely roamed the earth alongside animals and men. There were giant demons with hooves and twisting horns, demons with wings and with snouts blunted at the nose and dripping venom from their razor-sharp fangs, demons with chalk-white skin and ruby eyes that would suck the blood from their hypnotized victims, demons of bone and sharp angles, and many more than any man could possibly imagine. Yet for all these differences, all the peculiarities unique to each clan, one hobby united them all: disseminating pain.
These were creatures of chaos, of war, and catastrophes invariably followed them wherever they went. Some delivered the bubonic plague much as one would offer toys to children, while others simply decimated any populations unfortunate to stand in their wandering paths and left the remnants to deal on their own with the hygienic issues resulting from the carnage. Some, however, delighted in producing more subtle forms of misery: either through torture or mating, they forced their own uniqueness onto humans, forced all manners of mutation. If perchance their victims survived the ordeal, they would observe the results of their experiments with an infernal laugh before leaving the monstrosities to their fate. While some were so hideous that they were slain upon sight, others were either powerful enough or resembled humans enough that they were allowed to live, heavily bearing the burden of their parentage in a lifelong bid to survive.
This persisted until one day a human arose with two such deformities. One was the Mokuton, the ability of wielding water and earth simultaneously to yield wood. The other was the Byakugan: silvery irises with no pupil. Through these eyes he was able to see the demons' trickery for what it was: simple chakra usage. He assimilated their techniques and roamed the land to remove the demon population while spreading his teachings so that another may take up his task of he were to fail.
Through this endeavor he would eventually gain from one of his foes a new doujutsu, the Rinnegan. The jutsus associated with the doujutsu were of such power that it would earn him the title of the Rikudou Sennin, the Sage of Six Paths, a man who would forever be remembered in legend first as the Scourge of Demons and later, when the era of demons faded from Humanity's forefront as memories were wont to do, the father of ninjutsu.
However, just as the memory of demons dissipated into naught, the one great resistance the hordes of Demons put up was also lost with the passage of time, and men also forgot all about a group that refused to pass away so easily. These were the animal totems, animals that had grown beyond their limitations, animals that had transcended the boundaries of both size and power. Some of these clans recognized the error of the Demon ways and yielded themselves to Summoning Contracts subjugating them to the service of humans, and some even fought among themselves to spread the way of peace.
There were however twelve who refused to tame their ways, who denied their defeat. Pushed to the edge, they did the unthinkable: the Twelve Legendary Clan Heads met to discuss an alliance of Demons. These Twelve Head Clans were by far the most powerful of their Clan and the very embodiment of the animals they represented: the Rats with their keen wit, the Oxen known for their determination, the Tigers with their unparalleled control over fire, the swift and numerous Hares, the Dragons with their might and power, the calculating and analytical but deceptive Serpents, the Horses with their infinite stamina, the quiet Rams known for their bull-headedness, the mischievous and clever Monkeys, the Rooster usually rejected for their overbearing self-righteousness, the Dogs and the impossible good luck on their side, and the Boars with their infamous greed and the resulting power from the treasure-trove of techniques and gadgets.
After a long and passionate discussion, the Twelve reached an agreement. The Clan Heads would renounce their individual existence to merge together for the greater good of the Demons. Thus was born the Juubi, a mighty Ten-Tailed Demon. When the Byakugan user faced this new monstrosity, even he could not see the individual animals, though he knew which they were. All that stood before him was a Demon with an enormous, oppressive chakra, and abilities that dwarfed even his own. The creature's tenketsu system shifted faster than even his Byakugan could follow, while the chakra disruption blades which had served him so faithfully in the past now shattered before the foul energy of the beast.
More frightening, though was the doujutsu that surpassed his own in sheer power: dimensional vortices appeared at the Juubi's command and black flames, unquenchable in their thirst, morphed and warped almost as if alive, both protecting the Juubi from attacks as well as harassing he who would be known as the Rikudou Sennin. Gravity itself would obey the Juubi while various animals in the area would find themselves marked by the doujutsu and constrained to follow the Juubi's will and statues of demonic nature would erupt from the ground on a whim from the Juubi.
It was losing battle for the Rikudou Sennin. Not only did the Juubi possess the standard chakra techniques the Rikudou Sennin had previously seen, but there were also effects which seemed as magic even to him. Creating a concentrated fireball that did not disperse, forming dragons out of water, creating an impregnable lava wall; all this and more puzzled him. After the Juubi split itself into two creatures, each as ferocious as the other, the Byakugan user suddenly understood the mysterious new abilities of the Juubi. Each of the Clan Heads molded their chakra distinctively and had a few properties unique to their molding method. By combining the different chakra systems, they were able to collaborate to mold their distinctive chakra into new combinations, thus creating a more versatile and much stronger arsenal of techniques.
However, even with this new insight, the human was unable to match the raw power and versatility of the Juubi. With his back was pressed to the wall, he attempted a desperate gambit: in a huge burst of chakra, he summoned his own Mokuton abilities to simultaneously hold his opponent at bay with wooden stakes while retrieving the paper manuscript from the heart of his opponent. As soon as it was visible, he snatched it away from his opponent, and forced all of his Mokuton abilities to assimilate the scroll into his own body.
In an ear-splitting screech, the Demon finally yowled in pain for the first time since the start of the battle and flailed its ten tails in all directions while blindly throwing its chakra around, causing unprecedented destruction in its vicinity. The man held his ground and ever-so-slowly, his opponent's very soul leaked out of its solid shell in the form of ethereal strands of chakra that coalesced into a black miasma before seeping into the Rikudou Sennin. After the process finally completed successfully, the Rikudou Sennin possessed both the power and the abilities of the Juubi, thus marking him as the very first jinchuuriki. Without much effort, the remainders of the Legendary Twelve Clans were cowed into submission and agreed to the same Contract as the rest of the existing demons.
A long period of peace reigned afterwards. The Rikudou Sennin seized the opportunity to investigate the properties of each of the Twelve Clans' peculiar chakra system and devised a set of twelve handseals which would mold the chakra in the peculiar way of the original Clan Head. Once this was done, he wrote down the properties of each animal from his own experience, and also made sure to record the different combinations that had been used in the battle, as well as any he invented. One prominent addition manipulated the very time-space fabric of existence, which he put to use by rewriting each of the Summoning Contracts that held the Animal Demons in his thrall. Instead of binding them to follow him, he allowed them their peace far away until they were Summoned by this new jutsu he had devised.
After a while, the Rikudou Sennin grew restless even despite the monumental task and hand, and he took to travelling once again. He visited the lands he sought to protect when he first embarked on his journey, and was pleased to note the previously scattered families now formed into villages, and life in general was much easier and happier as a result. Wishing to further the progress, he helped these villages enter agreements with each other while continuing to spread his knowledge of the newly-baptized ninjutsu as well as liberally handing out Summoning Contracts to his more promising students wherever he went.
However, as he aged and his power waned, he slowly felt his control over the dreadful manuscript buried within his chest slip and the raging of the ten-tailed monster grow ever more agitated. He had no hope of defeating the monster if it were released even with the newfound knowledge: the difference in power between the two was simply too overwhelming. Therefore, the Rikudou Sennin settled for the best alternative: as keeping the tenant within his body forever or to send it to its death by dying himself were both beyond his abilities, he would separate the twelve entities and destroy the original manuscript once this was done.
First, to prevent the possibility of instantaneous fusion of souls back into the body of the ten-tailed Beast, he compacted the gigantic body into a ball and hurled it as far away from the Earth as he could, thus creating the moon. The strain from even this preparation was such that the Rikudou Sennin had to rest before attempting the next step. Unfortunately, even after recuperating for an entire week, this task proved impossible: even though he was aware of the characteristics of each Demon's chakra pathways, he was unable to discern where each one was within the tangled tenketsus spread throughout his tenant's jumbled chakra pathways, and analyzing the agreement between the Twelve Clan Heads proved as futile, for the Twelve Clan Heads had forsaken their identities even before they sat down to write the merger scroll.
In the end, he managed to tear the ten-tail apart into the Ichibi no Shukaku (one-tailed tanuki), the Nibi no Bakeneko (two-tailed cat), the Sanbi no Kyodaigame (three-tailed turtle), the Yonbi no Saru (four-tailed monkey), the Gobi no Irukauma (five-tailed dolphin-horse), the Rokubi no Namekuji (six-tailed slug), the Nanabi no Kabutomushi (seven-tailed horned beetle) and the Hachibi no Kyogyuu (eight-tailed ox), but was unable to separate anything else without it promptly returning to the remaining mass of chakra. Thus, he left the Kyuubi no Youko (nine-tailed fox) with the powerful doujutsu and with but a fraction less than a quarter of the Juubi's chakra. Most of the resulting tailed animals were entirely new ones, and even the Yonbi no Saru and the Hachibi no Kyogyuu were quite different from the mischievous Monkey and determined Ox that were merged into the ten-tailed demon.
The efforts left him drained, and while his nine tenants were less powerful even collectively than the ten-tailed beast, he knew that he could not hold these new demons inside him for long. All his life he had labored for peace in the world, and now in his death he would strive toward the same goal. Thus, he first detailed in a tablet his plans to deal with the Nine Tailed Beasts, the Bijuu, and then he called forth his most promising students: a Hyuuga, a Senju and an Uchiha.
To the Hyuuga, he extracted his own Byakugan, and yielded to him the divine task of keeping harmony through diplomacy. To the Uchiha, he advised actively enforcing world peace through force, the metaphorical "stick" to the Hyuuga's "carrot". To help them with this task, he offered a fraction the powerful doujutsu of the Kyuubi no Youko's eyes with all the supernatural abilities associated to it, even as the demon fox screamed itself hoarse. However, the Rikudou Sennin was careful to keep the ability to transfer powers, as he still had one more gift planned. As a result, the Uchiha was left with a dormant Sharingan while the Rikudou Sennin kept the Rinnegan which would have automatically activated the Sharingan. In his final act, the Rikudou Sennin gave his Mokuton powers to the Senju so that he may control the Nine Tailed Demons through their paper cores. His task done, the Rikudou Sennin left this world when nine Bijuu burst his chest open, giving birth to nine demons made of pure chakra without physical bodies to contain them.
For centuries afterwards, the Bijuu roamed the earth, wreaking havoc much in the vein of the demons of old until the sacred word of the Rikudou Sennin was lost in the flow of time. All of the Bijuu were at one point defeated and except for the Kyuubi, all were sealed into humans to form jinhuurikis. However, no one knew of seals powerful enough to potentially hold the Bijuu indefinitely, and breaking the vessel would invariably release the demon. Indeed, this was proven many times, and though many jinchuuriki died, nine Bijuu still existed. It was rumored in hushed tones amongst Sealmasters the world over that whoever would seal the Kyuubi would have found the formula to forever bind the Bijuu and subjugate the world to the Sealmaster's will. As it was, no one could devise a seal strong enough to hold indefinitely, and no one was powerful enough or sufficiently clever to seal the Kyuubi. No one, that is, until the Yondaime Hokage thrust the Kyuubi into a screeching toddler named Naruto Uzumaki.
Please review! I particularly welcome constructive criticism, no matter how harsh. If you find mistakes, please also point them out. Hopefully, I'll manage to make fewer of them in time.
Update: It was brought to my attention that I have been negligent in my dealings with the Rinnegan and Byakugan. I've brought some modifications to reflect my interpretation of events. It's stated in Narutopedia that the Rinnegan of the Sage of Six Paths may or may not have originated from becoming a junchuuriki for the Ten-Tails. I'm going to assume that it had and that the Sage had the Byakugan and the Mokuton before that. On top of that, I'll also assume that the Rinnegan/Sharingan combination is powerful enough to transfer kekkei genkais to another person. So in short, in this story, the Sage had the Byakugan, and the Juubi had a mix of Rinnegan/Sharingan. When the Sage absorbed the Juubi, he gained all three doujutsus. Just before he died, he transferred the Byakugan to the Hyuuga, the Sharingan to the Uchiha and the Mokuton to the Senju.