In 1920s Japan, forced by bullies to explore an eerie mansion, adolescent Nakahito inadvertently awakens the cyborg 'Steel Angel Kurumi' created by Dr. Ayankoji. A long-haired babe in a French maid's outfit, Kurumi proclaims Nakahito her 'master' and will accept orders only from him. However Kurumi is also an extraordinarily powerful robot sought by the military. The mismatched Nakahito and Kurumi, and Dr. Ayankoji and Nakahito's older brother Kamihito, find themselves drawn into a baroque plot involving a lecherous army general, various spies, and a second Steel Angel named 'Saki'.