Zuko, the spirit worlds local stray

The Final Act

No perspective, storybook author style

To Zukos's surprise the spirits he meets after that seem to take a liking to him much faster than he expected. Of course, he is sure to bring each a traditional offering which must have helped. They likely don't get many of those anymore, what with them being invisible to most people. 

He brings some of his uncle's tea herbal to the mountain spirits at the White Lotus hideout. They had already been mostly won over by Uncle Iroh but they appreciated the thought.

He brings native fruit to the koi fish spirits near Kyoshi island. They quite like it and, once the Kyoshi warriors realized they were spirits and not merely large fish, are now willingly brought some every week. They haven't had fresh fruit in centuries due to the plant's position near the center of the island and their preference to stay in the water so this really helped put Zuko in a good light. Aang however was still in some trouble as he rode them the last time they met, something that he apologized for this time around.

He brings some of the sun temple's eternal fire to the lava spirits that now occupy the ruins of avatar Roshu's temple. It was incredibly difficult to do but it's also the only thing that won't burn in their hands. They said that it tastes exquisite and found amusement in the young fire ones' panic when they first took a bite.

He brings egg custard tarts to the wind spirits at the abandoned air temple after learning it was a traditional Airbender pastry. He may be bad at making tea, and drinks in general, but he's always loved to bake with his mom when he was little so this was right up his alley.

He even visits some more far-out places to talk to elementals of all sorts. Lightning, ice, fog, and plant ones just to name a few. But with how vast the world is there are way too many to categorize. 

They all agree to fight alongside team avatar when the time comes and on the day of the eclipse, they deliver in full. 

When the Fire nation tries to advance the world itself comes alive around them and swiftly stops them in their tracks. Troops find the ground ripped from under them as lakes engulf soldiers and seaweed drags them down into the depths of the ocean. 

Gentle air spirits push down on soldiers with so much force that they have no choice but to stay on the ground, unable to even move a toe out of place.

When they do try to fight back the fire they make refuses to corporate with them. It takes a will of its own and burns supplies to the ground, leaving only ash in its wake.

The fire nation army is defeated before Aang even starts his battle with Ozai, something he told them to stay out of, and all without an enemy bender in sight. 

And that, children, is the story of how the spirits joined the war effort and a local stray became the Firelord.