Author notes: My lack of familiarity with the Avatar world will show much more with a long fic that actually has more than one character in it. I apologize in advance; this story is just for fun and is not designed to fit anywhere into Avatar continuity. Also I know nothing about Azula beyond the fact that she's Zuko's sister and has two hench-women. Please correct me if I've written her relationship with Zuko incorrectly, which I almost certainly have.
How Zuko Will Inevitably Join the Gaang
It was Zuko's bad habits as much as anything else that saved his life.
The fire was flashing towards his face, and it was almost automatic to draw his sword and use it as a focus to tame the flames. He was the sword and the sword's edge, and the enemy could throw fire at him until he or she went blue in the face. It would split and spill away from him-
It was then that he noticed the barrel of blasting jelly about three centimeters away from his face. It truly was automatic for him to roll sideways, behind the nearest bulkhead, and to cover his ears-
Which was downright stupid, because he wasn't on a ship and there was no bulkhead, and the sheer power of the explosion tossed him like a feather through two or three walls, and only his armor kept his ribs more or less intact-
And he landed on the back of the Avatar's flying bison.
There was something so ironic, so twisted in all of that; Zuko could hardly spare even a thought to laughing at the waterbender boy, who had inhaled half of his dinner and was choking, noisily and messily, all over the bison's saddle.
It didn't help that he was fairly sure that the person who attacked him was also the person who had taught him how to use a sword as a focus, how to protect himself as best he could from blasting jelly, and how to always, always wear his armor.
"Hi!" The Avatar chirped happily at him as the girl fussed over the boy. "Where'd you come fr-"
Zuko staggered quickly to his feet and half-fell, half-jumped off of the bison's saddle onto its head, next to the Avatar. As he landed (painfully), he was aware of two facts: He shouldn't let Azula near the Avatar, especially since she'd just tried to kill him again, and his honor rested on capturing the Avatar himself.
"Make this stupid animal move." He ordered. "Now."
"But why-" The question came from all three of the party's human members, and the lemur babbled something interrogative as well. They were all interrupted and answered by a large spear of lightning that demolished the building behind them and a sadistic giggle.
The Avatar went pale and with a sharp "Yip yip!" Appa rose ponderously into the air.
"So... will you teach me firebending?" The Avatar asked hopefully.
"...I will set your underclothes on fire at the first opportunity." How low he'd stooped. He had to resort to a silly childhood prank for revenge on his enemy.
"Cool!" The Avatar grinned. Zuko groaned. He just knew he was going to seriously regret not letting his sister take the Avatar when he'd had the chance.