Set in the fictional city of Teito in the late 1940s, it is a world where World War II never happened and the nobility system established in the Meiji Era still exists. An extreme divide exists between the upper and lower classes, with 90 percent of the country’s wealth being held by the upper class. The capital of Teito is in crisis with the emergence of a menacing phantom thief known as "The Fiend (Kaijin) with Twenty Faces" or simply "K-20." The film is based on The Story of Nijyumenso, a novel written by Soh Kitamura.