A possible concise summary is:
Alita is a teenage cyborg who was found in a junkyard by a doctor who gives her a new body and a name. She has no memory of her past, but she discovers that she was a powerful warrior from Mars who fought against the floating city of Salem. She falls in love with Hugo, a mechanic who works for a mafia boss who controls the motor ball sport and the murderous cyborgs. Alita becomes a hunter warrior and a motor ball champion to protect Hugo and to reach Salem, where her enemy Nova lives. However, Hugo dies trying to climb to Salem and Alita vows revenge.
Here are the key facts extracted from the text:
1. The story begins in the year 2500, 300 years after a war that devastated the Earth.
2. The city of Salem is a floating city where only the wealthy people live.
3. Iron City is a poor working-class city where survivors from all over the world live and work for the wealthy people of Salem.
4. Doctor Dyson is a character who collects used robot parts in a junkyard.
5. Alita is a teenager who is found in the junkyard by Doctor Dyson and is revived with a new body.
6. Alita's original body was destroyed, but her brain is still alive.
7. Doctor Dyson designed Alita's new body, which was originally intended for his late daughter.
8. Alita's body is a powerful cybernetic body that could power the entire city for many years.
9. The city of Salem is controlled by a mafia boss who rigs the motor ball game.
10. Hugo is a character who is a mechanic and is in love with Alita.
11. Alita becomes a hunter warrior and competes in the motor ball game to become a millionaire.
12. The mafia boss offers half a million credits to kill Alita before she can compete in the motor ball game.
13. Hugo is killed by a bounty hunter, but his head is saved by Alita and attached to a robotic body.
14. Alita infiltrates the mafia boss's base and kills him with her plasma sword.
15. Alita remembers her original mission to destroy the city of Salem and fights to stop it.
16. Hugo is killed again by a trap, and Alita is left alone.
17. Months later, Alita competes in the final round of the motor ball champions game, with the prize being the ability to go up to the city of Salem.