Avatar: The Last Airbender is often characterized as being a television show that treated its young audience with respect: its storylines were complex, its morality grey, and its lessons hard-learned. As a show with young teens and tweens as its main characters, dark, adult themes appeared but often only briefly. However, one particularly dark theme returned to the storyworld of Avatar in its subsequent series, The Legend of Korra: bloodbending.
Both The Last Airbender and The Legend of Korra operate in a narrative world in which certain individuals can manipulate ("bend") the elements to their will. In The Last Airbender's "The Puppetmaster," moral-compass Katara learns the dark variation of her waterbending: manipulating the blood within a person's body, known as bloodbending. This practice is portrayed by the animation as grotesque and grisly but only recurs twice more in this early series. When The Legend of Korra narratively fast-forwarded seventy years from the end of TLA, it also shifted the ages of its protagonists forward a few crucial years. The main characters are full-fledged teenagers and young adults. Correspondingly, bloodbending, one of the darkest themes of the original series, moved front-and-center in the Avatar narrative world. The season's villain, Amon, and a lesser antagonist, Tarrlok, are revealed to be bloodbending brothers, taught by their father, whose bloodbending is shown disturbingly in the video here.
The animation in LOK portrays bloodbending as torture: focusing on the pain and unnatural angles of Aang's body. The scene had many fans online--predominantly adults--exclaiming, "This is a kids' show?!" On one hand, yes, it is. It airs at 11am on Nickelodeon, but it's also a franchise aware of its adult fanbase and its own reputation as a show that doesn't sugarcoat its world: there is violence, poverty, and unkindness as well as nobility, community, and care. The Legend of Korra extrapolates the adult themes of The Last Airbender and positions them in a world slightly darker and for viewers slightly older. It meditates and repeatedly portrays the dark art of bloodbending. The darkness of the act is matched only by the adult nature of its punishment. The series ends with Tarrlok blowing up both himself and his brother, ending their father's line of bloodbenders. Fratricide and self-sacrifice underscore the adult nature of the bloodbending storyline, yet it's a conclusion that fits the unique world of Avatar as a franchise that treats its youth audience with the same expectations as its does its adult viewers.