Battle during Harmonic Convergence (9,829 BG)

The battle during Harmonic Convergence was a confrontation that occurred during the Harmonic Convergence of 9,829 AG between Wan and Raava, and Vaatu. The two sides fought for the fate of the spirit and physical worlds. The battle ended with Wan and Raava victorious, and Vaatu imprisoned in the Tree of Time, within the Spirit World. It marked the end of the Era of Raava.

Prelude
Ages before this Harmonic Convergence, Vaatu broke through the divide that separates the physical and spiritual worlds, allowing spirits to roam it freely. Humans, who were powerless against the spirits, took refuge in the shells of lion turtles who would protect them, eventually creating whole cities. In time, humans lost touch with one another, each believing their own city to be the only one in the world. Having won their previous duel, Raava kept Vaatu in check for almost ten thousand years. One day, Wan, who had been traveling the world after living among the spirits, came across the two after seeing animals and spirits fleeing from the valley where the two were fighting. Raava told Wan not to interfere in the business of spirits, but Vaatu manipulated Wan into using his firebending to free him from Raava's grip. After Vaatu escaped, Raava told Wan about the gravity of his mistake, and left in pursuit of Vaatu.

Continuing his travels, Wan discovered another lion turtle city, inhabited by people who would be given the power to control air when they would leave the gather food. Wan entered the city, and not long after his arrival, the spirits that lived there turned dark, and began attacking the city's denizens. Wan protected them, and was met again by Vaatu. A weakened Raava also arrived and was able to drive Vaatu away. Wishing to make up for helping Vaatu escape from Raava, Wan offered to help her, as she was getting weaker as Vaatu became stronger. Wan was bestowed the power of air to help, that Raava would hold for him until he used it. After Raava explained Harmonic Convergence in more detail, Wan and Raava visited other lion turtles to gather more powers and train during the year they had before the next Harmonic Convergence.

One day, Wan and Raava discovered human settlers, old friends of Wan, from his lion turtle city. Their meeting was interrupted by spirits, who were angry that the humans were destroying the forest. Vaatu's growing power allowed him to turn the spirits dark, and they attacked the humans. Wan tried to use all the four elements to stop the humans and spirits from fighting, but it was too much for him and he lost consciousness. When he came to, Vaatu told him all the humans had been slaughtered. Raava directed Wan to the southern spirit portal, that would lead them to the place where Vaatu and Raava were to fight.

Battle
In the Spirit World, Vaatu arrived through the northern spirit portal. Wan challenged Vaatu to go through him before getting to Raava, and began firebending at Vaatu. Vaatu evaded his attack, slammed Wan with one of his tendrils, and fired a beam at him, all the while boasting about himself. Wan screamed to Raava that they had to merge, and doing so allowed Wan to use all four elements against Vaatu, gaining an advantage. Wan began to feel the side effects of hosting Raava for too long, but urged her that they had to defeat Vaatu no matter what. Vaatu pinned Wan to the ground, sensing the Harmonic Convergence about to begin. The planets aligned, and the portals merged, marking the beginning of the Harmonic Convergence. Wan reached for the portal, and its energy flowed into him, permanently merging his spirit with Raava. Wan began attacking once more, and managed to trap Vaatu using all four elements, before imprisoning him in the hollowed section of the Tree of Time.

Aftermath
Wan closed the northern spirit portal from inside the spirit world, and guided the spirits in the physical world back to the Spirit World through the southern portal, and closed it as well, so no human would ever be able to physically enter the Spirit World and free Vaatu. With the spirits no longer roaming the world, the lion turtles denounced their roles as protectors of humankind, and stopped giving them the power of the elements. Wan, as the Avatar, would act as the bridge between the two worlds, and use Raava's power to keep peace. The advent of the Avatar, the closing of the spirit portals, and humankind leaving the protection of the lion turtles changed the world completely during the following ten millennia.