It happens slowly, the drifting apart. Of course they were already two individuals, but now silence and discord creep into the air between them. Katara is visibly angry at times, while Aang focuses only on the work, acting as though nothing is wrong.
One day Zuko overhears them arguing, Katara's voice rising and falling against Aang's even murmur. Zuko doesn't mean to, but he has paused in the shadow of a pillar and he is holding his breath.
"I know what you're saying, Katara, and I understand how you feel, but I... I'm the last. It isn't just about children. These women are genuinely trying to bring back airbending culture."
"Aang..." A heavy sigh. "Some things about airbending culture I don't think I can ever... ever... be a part of. This is not how we do things in the Water Tribe."
"I chose you once over the Avatar state, Katara. Please don't ask me to choose you over the Air Nomads."
"I never asked you to choose me over anything!"
Zuko feels a sudden ache in his body, his blood throbbing. He can hear ripples splashing in the ornamental pond where the Avatar and his Ambassador are having their discussion.
He resumes his walk and tries to pretend he doesn't understand. No one questions the rebuilding of the air temples and the expansion of the shrines. Dotted around the earth kingdom, they act as orphanages and refugee camps. A significant portion of Fire Nation revenue goes toward their support.
Everyone's heard the rumors, of course, of the Avatar's efforts to revive airbending culture. In the Fire Nation in particular, the Airbending Acolytes are a lewd joke. Everyone knows about them...
Zuko had thought that they were nothing but exaggerated rumors. Any truth to them would be... impossible.
But he knows how charismatic the Avatar can be. And Aang isn't a boy anymore but a young man, tall and strong and full of determination.
Things are impossible until Aang decides to do them.