Hope more people join, but here's a few prompts for now
Aang/Katara, children
Aang/Katara, moving on

Sokka/Suki, the battle isn't over
Sokka/Suki, marriage

Zuko/Mai, crush
Zuko/Mai, halting
Zuko/Mai, path not chosen

Aang/Zuko, bending
Aang/Zuko, dancing
Aang/Zuko, peace be with you

Zuko/Sokka, atonement

Sokka and Katara, brother

Iroh, loss
Iroh, struggle
Iroh, song unsung

Azula, fear
Azula, aftermath
Azula, reunion

Ty Lee, friendship
Ty Lee, colorful

Ozai, without power

Sokka, respect

Zuko, sacrifice