Woke Culture is getting out of hand. A live-action remake was bad enough, but they also had to change Astro Boy's gender.

cough

Ok,I'll try to summarize everything the best I can.

The Machine Girl: an high school girl's friend and her brother get killed by a group of bullies. Turns out they're part of a ninja-yakuza family.
When she tries to track them down,she gets her arm cut.
Then she manages to get help from a kind mechanic where she gets her arm replaced with a mechanical one,which can turn into a machine gun.

She finds the bullies and kills them and in the final part she has to fight against the bullies families who are also horrible people,(with their victims photo on their chest). Ultimately kills them one by one with the help of the mechanic,same for the high ups of this yakuza family(where the final boss,the mother,has drill tits).

Shyness Machine Girl:,the one in the gif,is a sequel/spin-off,where it kinda follows the same premise where a dear one dies,followed by revenge.
Some of the villains comeback,the protagonist is another girl who's shy,but because of this she can activate her weapons,in particualr the one shown here.because it makes it easier.

The villains are bulletproof now that they came back to life.