Mutonchaku Osananajimi Mechanic-chan無頓着幼馴染みメカニックちゃん; Clueless Childhood Friend Mechanic-chan

Long ago, alien creatures appeared in their town. Her childhood friend boy shielded Mechanic-chan and lost both arms in the process. She also lost her left arm at the time, but in order to repay the boy who protected her, she became a mechanic, and is now building his prosthetic arms.