It is great thread, I often thought about it, but it is stll mystery.
Anyway I think that Sage of six paths beat/sealed Juubi thanks Sealing jutsu amplified by Sage chakra.
My theory is that:
#1th. Sage of six paths was priest, who possesed Byakugan(he maybe half Uzumaki and half Hyuuga if clans areleady existed or if no then he simply has Byakugan). Byakugan let Sage of six paths discovered spiritual and physical energies which mixed together created chakra, later Sage of six paths created Sealing jutsu to stop Juubi as he found out or guessed that killing it would be impossible.
#2th. Sage of six paths as priest was meditating very often, and after discovered chakra made from Spiritial and physical energies, he was always aware/guessed about nature energy exisitng everywhere around of him, in plants, animals , air, water etc. Somehow Sage of six paths discovered way to draw this Natural energy into himself and thanks to his perfect chakra control, he was able to balance all: Spiritual, Physical and nature energies creating Sage chakra.
#3th. Sage of six paths taught then Senjutsu to his personal summons: Current Great Sage snake and Current Great Sage Frog. He discovered then that Chakra or sage chakra can be converted in five of basic nature manipulation: Fire, earth, wind, lighting, water. Later he created all his today known treasured weapons in preparations to fight against Juubi.
#4th. Finally Sage of six paths came to stop Juubi, Juubi was literally God, which Sage of six paths fast found out, while trying to harm it with his banana fan, his own five of basic nature manipulation: Fire, earth, wind, lighting, water and thanks to his unreal speed, unreal strength, unreal reaction time, unreal durability which were amplified by Sage chakra he could fight against Juubi for short time without dying. However soon he understood that fighting against Juubi is senseless so then he used Hyuuga technique to paralyze Juubi for second somehow then used powerfull Sealing jutsu amplified by Sage chakra on Juubi, becoming first jinchurki.
#5th. After becoming Jinchurki Sage of six paths decieded to use his Ying-yang release(power to create possesed by juubi) to create his two sons or he simply married some normal woman who gave born to two their sons. Unfortunetly first elder son was born before Sage of six paths could took control over his occular power(Juubi nine tomoe eyes), these cause first son to posses mutated eyes and strong spiritual energy, then Sage of six paths finally took control over his occular power and filtered them, cause Sage of six paths to got Rinnengan. His next son was born after SOSP got Rinnengan(having control over his occular power), so his second son recieved powerfull physical energy, strong body, great amount of chakra and ability to sense nature energy.
#6th. At his deathbed Sage of six paths chose Younger son to be his sucessor knowing that elder son recived some Juubi traits which can infulence him. Enraged Elder son left with younger son as Sage of six paths devided his Juubi in nine tailed beats, and sealing Juubi's corpse along with his body flying into space then creating moon in which he sealed himself.
#7th. Later Sage's sons began to continue their linage, creating Uchiha and Senjuu while forgetting about their famlily(Hyuuga and Uzumaki clans), Before Uchiha and Senjuu clan was created as we know together both Sage's sons fought against each other.
What do you think about my theory, guys ?
Sorry for my bad english
Problem with my theory is that: Sage of six paths would have known some secret to Byakugan which could let him discover way to convert his chakra to five of basic nature manipulation: Fire, earth, wind, lighting, water and somehow discover nature chakra.
