A historical story using Ghosts to explain the life times of the reign of Emperor Hirohito.Showa-shi by Shigeru Mizuki, is volume (1) in the series.

It describes an era of upheaval and impoverishment in Japanese history, beginning with the Tokyo Earthquake of 1923, and covering the financial panic, the Great Depression, the March 15th Incident, and other events up until the Manchurian Incident (1931)

(Source: Volume 1 Cover, 1989 release).