In the year 2263, Earth faces dire ruin from a catastrophic interplanetary conflict known as "The Fall" or "The Great War." Fast forward 300 years, in the bustling junkyard city of Iron City, a determined scientist named Dr. Dyson Ido makes a shocking discovery: a disembodied female cyborg that still houses an intact human brain. He decides to attach a new cyborg body to this brain, naming her "Alita" after his deceased daughter, the initial inspiration for the body.
When Alita, portrayed by Rosa Salazar, awakens, she encounters Dr. Chiren, Ido's estranged ex-wife, and strikes up a friendship with the charming Hugo (Keean Johnson), a conflicted scrap dealer who yearns to escape to the affluent Zalem, the last prosperous city remaining. Hugo introduces Alita to Motorball, an intense gladiatorial sport where cyborgs battle for supremacy. Unbeknownst to her, Hugo is secretly robbing cyborgs for their parts to appease Vector, the ruthless owner of the tournament, hoping to build an unbeatable champion.
Meanwhile, Dr. Chiren seeks Ido's assistance in creating cyborgs for Motorball, but Ido steadfastly refuses, leading Chiren to work covertly for Vector. Hugo believes it's possible Alita once hailed from Zalem, as all refuse in Iron City originates from there.
One fateful night, Alita follows Ido and discovers his true identity as a Hunter-Warrior. They become entangled in a battle against three cyborg serial killers, led by Grewishka (Jackie Earle Haley). In a fierce showdown, Alita instinctively uses her martial arts skills, dubbed "Panzer Kunst", to fend off attacks and protect Ido. Despite her newfound prowess, Ido advises against her desire to become a Hunter-Warrior, revealing the pain of losing Alita's original form to a rogue cyborg.
The plot thickens as Grewishka, working for Vector, seeks revenge and embarks on a quest to capture Alita, who later discovers a high-tech Berserker cyborg body in a crashed spaceship outside the city. Despite its formidable combat abilities, Ido refuses to let her install it. Frustrated and determined, Alita registers as a Hunter-Warrior. At the Kansas Bar, she and Hugo struggle to recruit allies against Grewishka, only to clash violently with the arrogant Zapan (Ed Skrein).
Amid the chaos, an upgraded Grewishka challenges Alita to a duel, escalating the conflict as he reveals connections to Vector. Though heavily damaged in their fight, Alita’s spirit remains unbroken, and with the help of Ido and Hunter-Warrior McTeague, they force Grewishka to retreat. Seizing an opportunity, Ido fulfills Alita's desire, transplanting her into the advanced Berserker body.
In her new form, Alita's memories resurface, including her mission to defeat Nova—the overlord of Zalem. Alita's love for Hugo prompts her to join a Motorball tryout, aiming to win the prize money to help him reach Zalem, despite Ido’s warnings of the lethal competition she faces. When Hugo's secret life leads to a catastrophic confrontation, Alita must decide between saving him or adhering to the harsh Hunter-Warrior laws.
Alita’s fierce love and determination ultimately inspire Chiren to betray Vector, allowing her to save Hugo in a desperate act of loyalty. Battling against Vector and Grewishka, Alita uses her new nanomolecular body to secure victory and confront Nova—the mastermind behind her struggles.
As the climax unfolds in a breathtaking chase, Alita pursues Hugo, desperate to save him, but she watches sorrowfully as he plummets to his demise, realizing the depth of their bond even in tragedy.
The narrative concludes with Alita, now a celebrated champion of the Motorball tournament, defiantly vowing revenge against Zalem as she locks eyes with Nova, who waits eagerly from above. "I will take you down," she declares, pointing her sword skyward, igniting a spark of hope and fury in the hearts of her new world.
