Yonezawa Domain
Amakasu was born in Miyagi Prefecture as the eldest son of a samurai of the Yonezawa Domain under the "bakufu". The caste system in Japan where society was divided into merchants, artisans, peasants and samurai was abolished in 1871 as one of the Meiji era reforms, but long afterwards, caste distinctions persisted with those of the samurai caste being disproportionately over-represented in the officer corps of the Imperial Navy and Army right up to 1945. Amakasu was educated in military boarding schools in Mie Prefecture and Nagoya, and entered the Imperial Japanese Army Academy in 1912. After graduation, he served in the infantry and then the military police in various postings in Japan and in Korea.