Legend of Korra:
The Legend of Korra is a spin off series to the original series Avatar the Last Airbender.
The first season, Book One: Air, sees Korra move from her secluded upbringing at the South Pole to Republic City to learn airbending from Tenzin, Avatar Aang's son. She enters the pro-bending league, and befriends the brothers Bolin and Mako, the latter of whom she eventually falls in love with, as well as Asami Sato, heiress to Future Industries. The ambitious politician Tarrlok enlists Korra to fight the anti-bender uprising of the "Equalists", led by the masked Amon, who strips benders of their abilities. Eventually, exposed as the son of a blood bending crime lord, Tarrlok reveals Amon to be his older brother. Korra and her friends, aided by police chief Lin Beifong and United Forces general Iroh, manage to unmask Amon to end the Equalists' military coup.
The second season, Book Two: Spirits, is set six months later with Korra learning that restless spirits called Dark Spirits have been terrorizing the south seas. Feeling that she can not learn to calm the Dark Spirits through Tenzin, Korra turns to her uncle Unalaq, the Northern Water Tribe chief, for guidance. However, as civil war among the Water Tribe branches erupts from the Northern Tribe's forced occupancy, Korra learns that the exile of her father Tonraq was arranged by Unalaq who is using her to achieve his own agenda which she learns is connected to her most distant past life: a young man named Wan who became the very first Avatar by permanently fusing his own life-force essence with the light spirit, Raava, to defeat her dark counterpart Vaatu, imprison him in the Tree Of Time, and closed the portals to the spirit world for ten thousand years.
Despite Korra and her friends attempting to stop him, Unalaq succeeds in freeing Vaatu from his prison, and merges with him to become the "Dark" Avatar that manages to purge Raava from Korra and destroy the light spirit. However, Korra is able to absorb energy from the Tree Of Time that allows her to fight the Dark Avatar, and with the help of Tenzin's daughter, Jinora, she manages to reclaim the reborn Raava while severing the light spirit's connection to Vaatu, and destroys him with Unalaq killed in the process. After the battle, Korra re-fuses with Raava, but because her connection to her past lives was lost as a result of her brief separation from Raava, Korra keeps the spirit portals open so that humans and spirits can coexist as a new age begins.