Ginta is a Japanese high school boy who often fantasizes about a land known as Mar Heaven. One day, he is mysteriously summoned to the imaginary land, which in fact turned out to be real. Upon reaching there, he learns of powerful weapons known as Arms that exist in Mar Heaven. With the companions and friends that he meets during his travels, the group seeks to destroy the Chess, a faction led by the mysterious Phantom, which is determined to bring about Mar Heaven's Ultimate Demise for reasons unknown.

Due to poor grades , Tsukune Aono, an average high school student, has been unable to get accepted into any private academy of his choice. By exceptional accident, the only school to accept him turns out to be anything but ordinary; the school is attended by youkai disguised as humans. Fearing for his life, he attempts to escape only to meet Moka Akashiya, a beautiful girl who just happens to be a vampire. Despite this, Tsukune decides to stay at the academy, hiding his human nature from students and teachers. Tsukune also discovers that when the rosary around Moka's neck is removed, her true nature emerges.

After leaving the North Pole , Aang finishes mastering Waterbending under the instruction of Katara, who has mastered the element faster than he has. Aang and friends travel to the Earth Kingdom city of Omashu to master Earthbending. Their initial plan is to learn under Bumi, king of the Earth Kingdom city of Omashu, but they discover that he and Omashu have been captured by the Fire Nation and Bumi is waiting for the right time to strike. Searching for a new Earthbending teacher, the group meets Toph, a blind Earthbending prodigy who becomes Aang's second teacher and teaches him, amongst other things, her unique ability to use earthbending to "see" vibrations with her feet. After discovering a hidden ancient library, the heroes discover information about an upcoming solar eclipse which would deprive the Firebenders of their bending and open to invasion, giving Aang his chance to defeat the Firelord. They struggle to reach the Earth King with this vital information, but are detoured by Appa's kidnapping. Azula, Zuko's sister, and her two friends Mai and Ty Lee chase the group as they struggle to reach Ba Sing Se, the Earth Kingdom capital. By capturing and then impersonating the Kyoshi Warriors, Azula engineers a plan to manipulate a secret group of earthbenders called the Dai Li to instigate a coup d'état that allows the Fire Nation to take complete control over Ba Sing Se and deal a fatal defeat to the Earth Kingdom, and destroys any hope of the Earth Kingdom staging a large-scale invasion of the Fire Nation. In a final confrontation, Azula kills the Avatar using lightning while Aang is in the Avatar state. By a last minute betrayal by Iroh, Katara is able to escape with Aang's body. Thinking the Avatar is killed, the world begins to believe there is no hope left. In reality, the Avatar has been revived by Katara using water she had received from their water bending master which contains special properties that amplify her natural water bending healing powers.

One hundred years before the start of the series , a 12-year-old airbender named Aang  learns he is the new Avatar, the only person in his generation capable of manipulating all four elements to his will and the one tasked with maintaining peace between the Four Nations of the world. Fearful of the heavy responsibilities of being the Avatar, coupled with the coming separation from his beloved mentor Monk Gyatso (to complete his training), Aang flees from home on his animal guide, a flying bison called Appa. Caught by a fierce storm, they crash into the ocean, and Aang's protective Avatar State freezes them in a state of suspended animation inside an iceberg. Right after his disappearance, Fire Lord Sozin, realizing that according to the Avatar cycle the next Avatar will come from the Air Nomads, launches a genocidal campaign against the Air Nomads. This way he can ensure that the next Avatar will not try to foil his plots for world domination as the last one of his kind.

The ancient kingdom of Parro has been invaded by the armies of Mongaul , and its king and queen have been slain. But the "twin pearls of Parro," the princess Rinda and the prince Remus, escape using a strange device hidden in the palace. Lost in the Forest of Rood, they are rescued from Mongaul soldiers by a strange leopard-headed man named Guin, who has no memories except for the word "Aurra."