Sokka is here as well. Together with Katara and a few of the Fire Nation's best (remaining) engineers, they design a ship that uses fire and water together to travel faster than any other ship their world has ever seen.
The ship doesn't just power through the water, it... swims.
Even sharing the design with the Water Tribes and the Earth Kingdom, more speed means more wealth. Even Zuko's most recalcitrant and isolationist ministers are beginning to see the benefits of cooperation as their pockets swell.
Sokka's humor has matured into something quiet, sharp, and fierce. When he deigns to acknowledge the Fire Lord, he regards Zuko with a nod, which Zuko has come to see as typical of the Southern Water Tribe. They are peasants who somehow see true royalty as beneath them.
Katara's glances at him are triumphant and radiant. It's working. Finally, the peace they won is working and everyone can see the results.
She beams at him and Zuko grants a small smile in return.
Something is going right at last.
He knows that disaster must soon follow.