Book 0: The Return of the false avatar

King Koenma prophesized the air nomad genocide and decided to recruit a powerful bender dubbed "the false avatar" Yun.

He sees Yun regretting his past choices and decides to give him a chance to redeem himself. What will happen when the "false avatar" and "the boy in the iceberg" work together to save the world from the fire nation and fight against their spiritual ally, Vaatu, the conqueror?