Avatar: The Last Airbender/Recap/Book 1/20 The Siege of the North Part 2

""I don't need luck though, I don't want it. I've always had to struggle and fight and that's made me strong. It's made me who I am.""

With his body kidnapped by Zuko, and his spirit adrift in the Spirit World, Aang tries to find the Ocean and Moon spirits to ask for guidance and protection. Instead he finds himself facing the mysterious Face Stealer Koh, the only one with information on the spirits' true forms and location. Aang is able to return from the Spirit World, and his soul is sucked back towards his body, forming a streak of like which Sokka, Katara and Yue (riding Appa) use to track him. They defeat Zuko, but Aang insists on taking him captive instead of leaving him to die.

When they return, however, the Fire Nation have penetrated the walls of the city, and Zhao's mad plan is revealed. He has reached the Spirit Oasis, and despite Iroh's warning that trifling with the natural order of things could have serious consequences, for all people and not just the Water Tribes, Zhao kills the Moon Spirit, causing a lunar eclipse and rendering Waterbenders powerless. Iroh, furious, attacks Zhao, who flees, Zuko in hot pursuit. Aang, in Avatar State, merges with the Ocean Spirit, forming a huge anthropomorphization of water ("Koizilla"), which clears the Fire Nation attackers from the city and then, still unsatisfied, flattens the Fire Nation fleet.

Iroh, trying to salvage things at the Spirit Oasis, notes Yue's white hair. Yue reveals that she was a stillbirth, but when her parents plunged her into the waters of the oasis, the Moon Spirit gave her part of its spark of life. She decides now to give that spark back, despite Sokka's protests. She bids him farewell as her body dissolves into moonlight, reviving the slain white fish that is the Moon Spirit. As the moon appears in the sky, Zhao loses hope, and when Koizilla comes for him, he surrenders to his fate, disdaining Zuko's offer of assistance. He disappears into the water, never to be seen again.

As the Gaang reunite and discuss their upcoming plans for the next season, the Fire Lord rants and raves about Zhao's incompetence and gives unspecified commands to his latest Dragon: his daughter Azula.

Tropes:

 * Ascend to A Higher Plane of Existence: Yue's connection with the moon allows her to become the moon spirit when the original dies.
 * Berserk Button: Harm to the spirits is one for Iroh.
 * Bittersweet Ending: The fire nation has been repelled and the day is won. But at the cost of Yue's life to Sokka's dismay. Meanwhile Zuko and Iroh are unaware they've been branded traitors by their nation and a much worse threat than Zhao is on the horizon.
 * Bloodless Carnage: The invasion itself. After Koizilla wipes out the fleet, we never see any dead bodies; considering Zhao's fate, that hints at a rather horrifying possibility for why they're all missing.
 * Casual Danger Dialogue: While Iroh and Zhao are discussing their strategy on their ship, Hahn interrupts, charging at Zhao, who casually tosses him overboard and resumes the converstation with, "As I was saying..."
 * Chekhov's Gun: Wan Shi Tong's library is brought up by Zhao.
 * City of Canals: The Northern Water Tribe's city.
 * Curb Stomp Battle: Aang combines with the Ocean Spirit and utterly destroys the Fire Nation fleet.
 * Deliberately Monochrome: While Zhao has the Moon Spirit captive and after he kills it. During the Moonless sequence, the only color comes from firebending and Yue's irises -- in other words, supernatural sources. This tips off Iroh to Yue's true nature.
 * Face Stealer: Trope Namer. And my, is Koh creepy.
 * Fan Nickname: Koizilla.
 * A God Am I: Zhao does this after capturing the Moon Spirit.
 * Karmic Death: Zhao is killed by the Ocean Spirit.
 * Meaningful Name: 'Yue' is Chinese for 'moon', which fits how the moon spirit gave energy to save her life as a baby. It becomes all the more fitting when she literally becomes the moon.
 * One Winged Angel: Koizilla
 * Red Sky Take Warning: While Zhao has the Moon Spirit captive, the moon's light turns red.