Prologue
Aang
Sometimes, the connection between the spirit world and the physical world is so complicated that even the Avatar isn't capable of understanding it.
Growing up at the Southern Air Temple, I was always taught that the Avatar was the bridge to the Spirit World. But, I was also taught that Spirits were amongst us benders and non-benders in strange ways. When I was travelling the world with Katara and Sokka, I witnessed this repeatedly. There was Hei Bai, the spirit of the forests that the Fire Nation destroyed during the war, who kidnapped the people of Senlin village for revenge. Another was Wan Shi Tong and his Spirit library in the middle of the desert.
There was also Yue. She was blessed with life by the Moon Spirit, Tui, when she was a newborn baby. When she was sixteen years old, she gave it back in order to maintain the balance between the moon and ocean after Admiral Zhao slayed the mortal form of Tui.
When I left the North Pole after the battle between the Water Tribe and the Fire Nation, after Yue's death, I didn't realize that Yue's sacrifice was incomplete. I didn't know that the balance between the moon and ocean had been shifted when Yue replaced Tui and she was not the equivalent opposite to La.
If I had realized, I would have done something. But what?
Nothing. There was nothing I could do to fix it. The Avatar's responsibility was to keep balance and peace between the four nations. Not to keep balance between the spirits of opposites.
Atleast, that's what Shio told me. And everyone else.
I still feel like I should have done something. I feel like I had carelessly started a wild fire, and when I realized it, it was too late and I couldn't do anything to stop it.
That's how I saw it. And I think that's how I'll always feel, even when the whole thing is forgotten by mankind.