Watch The Machine Girl
A young woman named Ami attends college and is happy. Except she must mother her younger brother; both their parents are dead. Her brother has a dangerous debt problem, owing lots of money to another boy. A boy who is next in line to head a violent ninja-yakuza gang. When her brother can't pay, they murder him. Ami sets out for revenge and is captured by the evil killers. While torturing her, they cut off her arm. She barely recovers enough to escape and is then befriended by machinists who construct a special gun-mounted replacement prosthetic arm. Now the real vengeance begins!