It's Happy Line

Story begins when the main character named Asami Hyuga witnessed his brother who died in a fall from the top of the building, police said the incident was a suicide, but asami are not satisfied with the information the police began investigating his own case the death of his brother. Asami finally know the cause of her sister's death from the diary of his brother, sister Asami was not suicide but was murdered by a bunch of unruly children who are still at school with his sister.
after knowing the facts behind the death of his sister, Asami filled with anger and intends to get revenge on the group that had killed his brother. Asami action began attacking the group, but unfortunately, it turns out the group's leader is the son of a Yakuza.
Asami defeated and mortally wounded and lost his left hand after a failure in the attack, Asami dying helped by a husband and wife owners of a parent workshop that his sister friend who was also killed, this is where Asami gain new strength of the left hand is transformed into a weapon by married couples workshop owner. and revenge began again the Machine Girl Asami.
The Machine Girl part 1
The Machine Girl Part 2