It might be an omegaverse, since that's the easiest reason for why Azula is the heir and not Zuko, even though he's older. I'm lazy,

The spirit and human realms were not separated, so the spirits play the role of the gods, kind of. Raava isn't in a person either. The title of Avatar is equal to 'hero,' especially a demigod.

#AzulaATLA #azutara #atla #avatarthelastairbender