This is the story of Zarkanna Zandra.
Daughter of Zadrine Zen-Lu of the Fire Nation and Hakoda, Chief of the Southern Water tribe.
Half sister to Katara and Sokka of the Southern Water Tribe.
Guardian and Spiritual right hand of the Avatar.
Love interest and (possibly) wife of Fire Prince Zuko.
Long ago, it was prophesied that a great war would bring the world to its knees and on the brink of chaos. The time for an Avatar would be direr than ever before. But he could not do it alone. This Avatar would need the help of one more skilled than he- one who descends naturally from opposing elements. Born of fire and water, this being would bear marks and show exemplary courage and strength. She and the Avatar would be connected through spirit and camaraderie. The prophecy was passed down through generations, and almost lost except at times when the world needed it for hope. This is that time. And the Chosen One has emerged.
(It's possible you'll see that in a future chapter. Maybe said by Iroh. It's not a well known prophecy. It's a little known "rumor" among common people. But it is known among people of dangerous power
aka- the Fire Lord, Rulers of the Water Tribes, Earth Kingdom, and people of dangerous influence there.)
The prophecy:
The Chosen One will be born.
Right hand to who by both worlds is torn.
She who will be once, twice blessed.
Moon and Sun she will attest.
Descended from past Avatar.
Born to end a deadly war.
Thrice mothered in her early life.
To son of fire she will wife.
She with hair like copper flame.
Fire and water she will tame.
Fates of nations lie within.
Both good and evil cannot win.