Kei is not my own. She is a brain child of @cyb-by-lang
How the hell did she get there? No idea! Maybe this is a dimension travel like the slider time-travel episode in the B-plot. Maybe this is more along the lines of "Whoops, found a hole in reality! Oops!" Maybe one of the great spirits got tired of waiting around for the damn avatar and decided to take matters in their own metaphysical hands, snagged Kei, and told her she's got a one-way ticket home, free of charge, if she can just muscle her way into fixing shit.
Now, for the big question:
For the simple fact that Isobu = not-a-lion lionturtle.
He's certainly big enough! He's got the intelligence and the hands (paws? flippers?) too! So... where are the lion bits????
He can't be a turtle-duck. Urchin-turtles never get that big either! He's the wrong anatomy for turtle-urchins, he can't possibly be an oyster-eel, and - wait, three tails? Ah! So he must be a whale-turtle with porcupine-spiritfox ancestry! Yes, that must be it!
(Isobu is not all that thrilled to have "fox" in his labeling. Aang does not listen. Of course that's what he would say! He's got spiritfox in him, after all! Jokes, pranks, and lies are par for the course. Look at him, being a good avatar! Well done, Aang!)
Kei + Zuko = tired babysitter club
Toph and Isobu are tiny terrors and also best friends. They make gigantic rock / coral statues of themselves together in various Amazing and Baddass poses. They also do piggyback rides on their respective Partner In Crime. (Don't worry, Isobu makes a mini-him clone first. Obviously. He's not too big for Kei to carry him Sokka.)
Kei must be a spirit. How tf else can she MAKE water out of nothing and then EXPLODE little bits of paper???? (Anybody else gonna mention that little fire trick she did? No? Yeah, okay, I didn't see a thing either.)
Kei, mostly to Zuko: "And then I just go like this..."
Aang: "Airbending?!?!" :o
Sokka: "No! Sword bending!!!" :D
Azula v.s. one singular shinobi who won't take any of her bs
Has Azula ever felt KI before? Has Ozai ever felt KI before? What about biju-fueled KI??
Life-changing field trip, anybody? It's time you learned the art of Not Giving An F
Ozai: "I could kill you anytime I want."
Zuko, very much not panicking, thank you very much (not that anyone could tell): "You're not special."
Isobu: "You sure I can't kill him? It'd be so easy too. I'll even be so generous as to let you pick the method."
Zuko: "Umm... Living is enough of a punishment for him."
Kei: "Well... There's an idea."
Kei: "Hey, we're planning out how to make the #1 Loserlord's life a living hell. You want in?"
Katara, grabbing a very thick folder from deep in her personal bag: "Do I ever!"