Every time it is discussed how the So6P had defeated the Juubi it is always brought up that he either had the Rinnegan or that he used some sort of Uzumaki fuinjutsu.
I believe that the So6P had some sort of sage mode that allowed him to sense nature energy and absorb the Juubi, because the Juubi is made out of nature energy and the So6P was strong enough to just straight up absorb the Juubi into himself.
I believe that the So6P had some sort of sage mode that allowed him to sense nature energy and absorb the Juubi, because the Juubi is made out of nature energy and the So6P was strong enough to just straight up absorb the Juubi into himself.