Avatar AU where Aang stays in the iceberg and Katara is mistakenly believed to be the Avatar after she “earthbends” a rock by moving the ice inside it.
Instead of telling the truth and letting everyone down, she and Sokka pull on an elaborate charade and go on a journey to convince the world that the Avatar is back.
Sokka was initially against the idea, thinking it’s crazy, but he got onboard anyway because it’s his little sister and he can’t let her go out into the world alone and put a target on herself.
After they started, he got super into the idea and started crafting an elaborate backstory for her Airbending predecessor, and devising ways for her to fake-bend the other elements.
The Road to Ba Sing Se. I love it.
Bumi agrees to teach her because he is pretty sure she’s a reincarnation of him
Sokka: But… you’re still alive.
Bumi: So is the real Avatar. I think we can bend the rules of reincarnation a bit.
Zuko still gets a redemption arc and switches sides. Only after he joins Team Avatar does he learn that Katara is not, in fact, the avatar. By this point he’s already committed so screw it he’s teaching a waterbender how to fake-firebend now.
That’s very in-character because Aang never wanted to be the Avatar anyway.
Sokka after learning the real Avatar was 20 minutes from his home village the whole time:
katara ends up developing various methods to seemingly manipulate the elements. the aforementioned bending of water in rocks. but also bending the water in air to create pressure difference to make wind. bending water to separate the hydrogen and oxygen of some water molecules while rapidly changing the temperature in others to create fire. she still learns bloodbending.