as far as energy bending goes. The lion turtle said "In the era before the Avatar we bent not the elements but the energy inside ourselves."
This implies that anyone can do it. And if it was before the Avatar then the avatar certainly isn't the only one who can do it.
I think it's more of an ability that was awakened by the lion turtle. Sort of like Zuko learning to bend from the sun and not from anger.
Also, an unbendable spirit, that seems like both will and charisma to me. But mostly will.
That's my take on it.
Yes, but was there humans in the era before the Avatar?
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