The Adventure really-begins when Avatar Korra and her friends, who-are sometimes called "Team Avatar": the bending brothers Mako and Bolin, her non-bender girlfriend Asami Sato and their four little-friends, who-are sometimes called "The Littles": Daniella and Dylan Spellman and Coraline and Max Jones are entrusted-with a mysterious sword called "The Sword of Darkness" (A Magical-Blade forded-by the Evil Sauron, Rumored-to belong-to "The Kingdom of Half-Moon's Missing Princess") and are drawn-into a threatened-world - the war-torn planet of Etheria - Struggling-to survive the two different forces who-are battling for control there (The Horde, with its skillfully trained soldiers and advanced technology, has one goal: to conquer all of Etheria in the name of it's leader. and The other force, the Rebellion, which-is made up of loads-of different-types of princesses and has been continually-fighting to push-out the horde and maintain harmony and freedom for all of Etheria's people.), Team Avatar meets one-young-girl who doesn't need a hero. In-fact, She is a hero.... Adora (A.K.A: She-Ra: Princess of Power! Who just so happens to-be Korra's long-lost cousin) and the leader of "the Princess Alliance", a group of other magical girls that all-oppose The Horde and it's wicked-leader, The Evil "Lord Hordak".
Upon-pledging their own-allegiances to their new-found friends, Hordak and army of soldiers meet the might of Team Avatar and the bravery of The Littles head-on! But their Second-in-Command and Adora's former best friend, Catra, seems to have a strange connection to The Sword of Darkness.
Weird! (And if Team Avatar thinks that's weird, it gets-weirder) Can this cat-like servant of the forces of evil be connected to the magical blade?
The film begins with a full-moon shining-over the "endangered-species-people"-inhabited the city of "Chichen Itza", one-of many in the "Kingdom of Half-Moon". at "The Secret Temple", the "Magicat" King Felix (Orlando Brown) and his wife the "Magicat Queen" C'yra (Tara Strong) are-meeting with the city's "animal-people-council" (Consisting-of) King Sidious (The Snake King), Queen Arachnida (The Spider Queen), King Leonidas (The Lion King) Count-Bat (The Bat King), Queen Merida (The Bear's Queen), Queen Beeanna (The Queen Bee), Master-Warsi (The Wolf King), Queen Antamala (The Ant Queen) and the King brothers Tigrus and Tigaris (The Twin-Tiger Kings) (David Spade, Eartha Kitt, John Goodman, Patrick Warburton, Jodi Benson, Dani Harmer, Tim Allen and Tom Hanks) just-as an "animal-sacrifice" is just-about to take place (That is Desperately-needed o prevent the end of the world from-happening, at the end of "the 13th Baktun" and "the Mayan Calendar"). just-then (Much-to the council and the king and queen's suspicions) a really-young (And-later revealed to-be both, the king and queens long lost-daughter and the entire-kingdom's long-lost "Princess of The Order of the Claw") Catra (Juliet Donenfeld) sneaks-up towards her surprised parents (and the surprised council) and shows-off a pig (Named Squeaky-Boo), (which she'd sneakily stolen) from the yard one-of the villages pig-wranglers "Mrs. Nightingale" (AJ Michalka, in a duel-role) and it's now being fattened up by the temple cooks, (showing that it-is ready-to be-sacrificed). Mrs. Nightingale hears about the pig's theft (from one-of her nearby neighbours) and attempts to rescue her prized-pig (to no avail). After the really-successful sacrifice (Much-to Mrs. Nightingale's Horror, Shock and sadness), the little-priest (who'd performed the much needed sacrifice), a lil-Magicat kitten named Cassandra (Danielle Kemp), discovers that the-world will-not end after the 13th Baktun (To the councils dismay but to the King, Queen and Princesses' relief).
some years later, Catra (AJ Michalka) has grown-up (living a sheltered-life in "The Fright Zone") to become a strong, independent, smug and sassy young-woman (despite her mistreatment in childhood, by her ex-guardian and superior Shadow Weaver (Lorraine Toussaint).) become the second-in-command and forced the evil Lord Hordak (Keston John) to agree to her dark-plans to end "the Rebellion" by removing his armor's crystal. But her emotional walls have-began to crumble (from a genuine guilt over what she's done). One-night (After another-one of her guilt inducing Nightmares), Catra walks-around the fright-zone (shivering, due-to the cold-weather outside her personal-quarters) and outside the horde base before she notices and bumps-into her new-protector "Double-Trouble" (Jacob Tobia, disguised-as a small-gray mouse). After Catra talks-to them all-about her nightmare and Double-Trouble realises that she's truthfully-admitting her guilt, Catra, terribly shaken by her frightening dreams (coupled-with an increasing full-body pain), embraces herself, breaks-down and starts crying (in her own-arms), admitting-to them (And to herself) that she's never felt so-terrified before because she'd never felt so-helpless. Double-Trouble comforts her, and-then afterwards they tell her that telling-someone about your dreams was "the first and most difficult step in overcoming the fears in her heart" then they explain-to her that "someone from another-world" will-come to Etheria (with "Her own-friends") and aid-her in redeeming-herself for her past but "You just don't know it yet.". after they leave, Catra falls asleep (thinking-about what they said).
The Next-Morning on a place that doesn't have etherian-magic called - Earth - Team Avatar's eldest-youngest member and the young-witch in-training Daniella "Dani" Spellman (Jessie Flower) wakes-up to the very-first-day of a brand new-term at her big-school "Republic City Middle School". after-both getting ready and getting all-dressed up, collecting her pre-packed lunchbox from her friend Avatar Korra (Janet Varney) and her Airbending-uncle Tenzin (J.K. Simmons, in a duel-role), her pre-packed schoolbag from her other-friend Mako (David Faustino) and her young-warlock-in-training little brother Dylan (Zach Tyler Elsen), her (Which-is Due-Today) book-report from her other-friend Bolin (P.J Byrne) and Dylan's best-friend Max Jones (Kath Soucie) and her new-broomstick from her other-friend Asami Sato (Seychelle Gabriel) and her own-best friend Coraline Jones (Dakota Fanning), Dani arrives-at the school-gates and lands-her broomstick on the schools-grounds (Just-Before the first School-Bell goes-off, starting the school-day). after she arrives, she's walked-up to her classroom by former publisher of the Daily Bugle tabloid turned the new-school-vice principle J. Jonah Jameson (Also, J. K. Simmons). while in the first-class of the first-day with her teacher Mrs. Maggie Woolingnatz (Katey Sagal) and her classmates, Dani learns-about Etheria, it's culture, it's people and all-of the planet's-history (Including the first-ones, the horde's arrival, the on-going war and "The Legend of the Magicat Princess") and-then Mrs. Woolingnatz excuses Dani from the rest-of her class because General Iroh (Dante Basco), President Zhu-Li Moon (Stephanie Sher) and her husband Varrick (John Michael Higgins) both-need her for "Unknown Reasons" (Upon receiving a message from the principles secretary).
- Janet Varney as Korra, the Avatar immediately succeeding Avatar Aang and the main protagonist of the series
- David Faustino as Mako, a firebender (who grew up on the streets of Republic City) and one-of Korra's friends
- P. J. Byrne as Bolin, an earthbender who, (along with his brother Mako), is friends with Korra
- Seychelle Gabriel as Asami Sato, daughter of Hiroshi Sato, President of Future Industries and Korra's Girlfriend
- Jessie Flower as Daniella "Dani" Spellman, Team Avatar's eldest-youngest member and young-witch in-training
- Zach Tyler Elsen as Dylandra "Dylan" Spellman, Team Avatar's young-warlock-in-training and Dani's little-brother
- Dakota Fanning as Coraline Jones, Team Avatar's young tech-genius and Dani's best-friend
- Kath Soucie as Max Jones, Team Avatar's young spy-boy, Coraline's little-brother and Dylan's best-friend
- J.K Simmons as Tenzin, the youngest son of Aang and Katara, an airbending master, Korra's Mentor and Dani and Dylan's Uncle / J. Jonah Jameson, Republic City Middle School's new vice-principle
- Mindy Stirling as Chief Lin Beifong, leader of the Metalbending Police Force of Republic City and is the daughter of Toph Beifong
- Maria Bamford as Pema, Dani and Dylan's aunt, Tenzin's wife and Mother-of Ikki, Jinora, Meelo and Rohan
- Kiernan Shipka as Jinora, the first child and elder daughter of Tenzin and Pema, Cousin of Dani and Dylan and granddaughter of Katara and the late Avatar Aang
- Darcy Rose Byrnes as Ikki, the second child and youngest daughter of Tenzin and Pema, Cousin of Dani and Dylan and the granddaughter of Avatar Aang and Katara
- Logan Wells as Meelo, the third child and the first son of Tenzin and Pema, Cousin of Dani and Dylan and grandson of Avatar Aang and Katara
- Dee Bradley Baker as Naga, Pabu and Bum-Ju, team avatar's three animal-friends
- James Remar as Tonraq, Korra's respected warrior father
- Alex McKenna as Senna, Korra's mother
- Dante Basco as General Iroh, the youngest general in United Forces history, the son of Fire Lord Izumi, the grandson of Lord Zuko, and the grandnephew of Azula and Kiyi
- Lisa Edelstein as Kya, the second of Avatar Aang and Katara's three children and their only daughter (as well as the couple's only waterbending child) and Dani, Dylan, Ikki, Meelo, Jinora and Rohan's aunt
- Richard Riehle as Bumi, Avatar Aang and Katara's first child and eldest son (as well as the only one to be born a nonbender among the couple's three children) and Dani, Dylan, Ikki, Meelo, Jinora and Rohan's uncle
- Anne Heche as Suyin "Su", the founder and leader of Zaofu, the daughter of Toph Beifong, and the younger half-sister of Lin.
- Alyson Stoner as Opal, Bolin's Girlfriend, an airbending member of the new Air Nation and the daughter of Suyin Beifong and Baatar, half-niece of Lin Beifong, and granddaughter of Toph Beifong.
- Zelda Williams Kuvira, a master metalbender (who served as political and military leader of the Earth Kingdom and the Earth Empire between 171 and 174 AG).
- Aimee Carrero as Adora / She-Ra (LaLa Nestor as young Adora)
- Karen Fukuhara as Glimmer, Princess of Bright Moon
- AJ Michalka as Catra (Juliet Donenfeld as young Catra)/ Mrs. Nightingale
- Marcus Scribner as Bow
- Reshma Shetty as Angella, Queen of Bright Moon
- Lorraine Toussaint as Shadow Weaver
- Keston John as Hordak, Horde Prime, Grizzlor, Additional Voices
- Lauren Ash as Scorpia
- Christine Woods as Entrapta, Princess of Dryl, and Octavia
- Genesis Rodriguez as Perfuma, Princess of Plumeria, Additional Voices
- Jordan Fisher as Sea Hawk
- Vella Lovell as Mermista, Princess of Salineas
- Merit Leighton as Frosta, Princess of the Kingdom of Snows
- Sandra Oh as Castaspella
- Krystal Joy Brown as Netossa, rebel princess
- Noelle Stevenson as Spinnerella, rebel princess
- Brenda Song as Peekablue, Princess of Crystal Cove
- Ashley Tisdale as Sweet Bee, Princess of Beegonia
- Demi Lovato, Selena Gomez and Bridget Mendler as The Star Sisters (TallStar, Jewelstar and Starla), triplet princesses of Galactica
- Aly Michalka (AJ Michalka's Sister) as Flutterina, Princess of Butterfly Bluff
- Adam Ray as Swift Wind
- Geena Davis as Huntara
- Morla Gorrondona as Light Hope, Additional Voices
- Grey Griffin as Razz, Additional Voices
- Chris Jai Alex as George, one of Bow's fathers
- Regi Davis as Lance, one of Bow's fathers
- Dana Davis as Lonnie, Additional Voices
- Antony Del Rio as Kyle, Additional Voices
- Jacob Tobia as Double Trouble
- Danielle Kemp as Casandra
- David Spade, John Goodman, Eartha Kitt, Patrick Warburton, Jodi Benson, Dani Harmer, Tim Allen and Tom Hanks as King Sidious (The Snake King), Queen Arachnida (The Spider Queen), King Leonidas (The Lion King) Count-Bat (The Bat King), Queen Merida (The Bear's Queen), Queen Beeanna (The Queen Bee), Master-Warsi (The Wolf King), Queen Antamala (The Ant Queen) and the Kings Tigrus and Tigaris (The Twin-Tiger Kings)
- Lindsey Lohan as Museum Guard / Mewsette, Dani's pet white-kitten
- Tobey McGuire as Dr. Samuel Cortez / Mewki, Dylan's pet tabby-kitten
- David Tennant as Captain. Kirk Saikan
- Katey Sagal as Mrs. Maggie Woolingnatz, Dani's teacher at school