Soon after Avatar Aang ran away from the Southern Air Temple and disappeared for one hundred years, the comet flew near the planet's orbit. Fire Lord Sozin took advantage of its passage to drastically enhance his firebending army's power and deliver a deadly first strike that plunged the world into the darkness of an all-out war of world conquest. This first assault resulted in the extinction of the Air Nomads, the sole exception being Avatar Aang. The Fire Nation later renamed the comet "Sozin's Comet" in honor of the Fire Lord's great victory.

One hundred years later, Avatar Roku's spirit warned Aang of the comet's return at the end of the summer. With its passing, Fire Lord Ozai would gain the power he needed to finish the Hundred Year War once and for all. This gave Aang less than a year to master waterbending, earthbending and firebending in order to defeat the Fire Lord and end the war; because if Ozai were to succeed, not even the Avatar could restore balance to the world.

When Sozin's Comet arrived at the end of the summer as predicted, it once again increased the firebenders' power one hundredfold, giving them the power required to eradicate the remaining earthbender rebellions. Fire Lord Ozai planned to use this opportunity to personally lead a fleet of airships to burn the Earth Kingdom to the ground with his enhanced powers. Team Avatar and the Order of the White Lotus were the only ones that still stood in his way, and launched a counterattack. The Order of the White Lotus took it upon themselves to liberate Ba Sing Se from the Fire Nation's oppression, while Katara and Zuko faced Azula at the Fire Nation Capital, and Sokka, Suki, and Toph were responsible for the destruction of Ozai's airship fleet. Aang challenged the self-declared Phoenix King Ozai at Wulong Forest in an attempt to end his world conquest.