Shoju (followers) was a category of slave that existed in Medieval Japan.
Shoju originally meant 'subordinates,' and those in this category were owned by nobleman, military families, temples, and shrines and propertied farmer and so on for servile labors, and were regarded as properties to be transferred or inherited.
There existed 'Genin' (underlings) as a close parallel to Shoju and two of them were often used in pair as 'Genin - Shoju'; generally, Genin meant the slaves of upper class farmers and were called 'Hyakusho Genin' (Genin of farmers), while Shoju meant the slaves of a military family and was called 'Jito Genin' (Genin of jito - manager and lord of manor.)
However, in practice, as those definitely in the class of Genin were sometimes called 'Shoju', the two designations were used interchangeably with no significant differences in usage.
As some Shoju even had their own independent households and families and cultivated their land independently, Shoju was not a uniformly established class, in reality. Shoju were descended from 'Kenin' (houseman) that existed before the Nara period, and usually belonged to the master's house by themselves from generation to generation. As Shoju were subordinate to the military family, they attended their master on the battlefields in wartime doing such labor as packhorse driving or carrying the enemy's head; nevertheless, they were not regarded as samurai warriors, and even if they carried the enemy's head, it was not considered as a military achievement.
After the early-modern times, the designation Shoju became gradually obsolete, while the word Genin became used frequently as a designation of slaves whether their masters were military families or farmers.