Anonymous:

i think mako would have to be a watertribesman, or at least an innate waterbender, for him to be the avatar in an au!! because of the cycle of the elements. aang was an airbender, and after an avatar who is an innate airbender comes an avatar who is an innate waterbender. so he'd have to be a waterbender or a water tribe member in order to be the avatar, not an innate firebender. at least i think that's how it goes!