Oniwabanshū

The Oniwaban (御庭番, garden guard^?) or niwaban (庭番^?) was a group of onmitsu government-employed undercover agents established by the 8th Tokugawa shogun, Tokugawa Yoshimune (1684–1751). They are sometimes described as "ninja".

During the Edo period, onmitsu (the term meaning a spy or an undercover detective) acted as secret agents in security and espionage functions, mainly intelligence and information gathering, sometimes with aid of kobushikata, small groups of lower-class agents posing as mobile manual laborers and working under Iga ninja supervisors. The oniwaban followed a strict set of regulations, which, in some cases, forbade them from socializing with the general public.

Tokugawa Yoshimune established the Oniwaban as an elite cadre of originally about 20 handpicked onmitsu, providing him with information about daimyō feudal lords and shogunate officials, while also protecting high-ranking officials of the government and acting as security guards in the Edo Castle. They were possibly quartered in the garden of the castle, hence the name.

According to some sources, during the tumultuous time of the Bakumatsu revolution the oniwaban were even sent to the United States to spy not only on the shogun's opposition, but on the Americans as well.

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