After her husband died in the Battle of Kawanakajima in 1561, Mochizuki Chiyome, a Japanese noblewoman, was approached by Takeda Shingen, a powerful feudal lord, to create an all-female ninja squad to secretly gather intelligence and correspondence.

To do so, Chiyome created a ninja school for young girls. According to Stephen K. Hayes in his book Legacy of the Night Warrior:

Chiyome established her underground academy in the village of Nazu, in Chiisa-gun of Shinshu (present-day Nagano), and went to work as the headmistress of her school for female ninja agents. Since the miko were always young unmarried girls, Chiyome Mochizuki began recruiting appropriate candidates from the ranks of the countless children rendered homeless by the all-consuming civil war that raged throughout the island nation of Japan.

To the outside observer, the school appeared to be the work of a compassionate woman trying to better society. However, the kunoichi, female ninjas, were trained in a variety of strange and sometimes brutal ways such as mind-set perception, which involved the girls meditating on their miserable pasts to become more loyal to Chiyome, their savior.

Besides loyalty training, the girls also learned proper information gathering techniques. For example, the girls were instructed on how to cause confusion, spread rumors, recruit reliable messengers, make disguises and even use their sexuality to manipulate men, reports Hayes.

Chiyome’s girls were so secretive that their existence wasn’t known until after Shingen’s death. Despite Chiyome’s legendary status, no one is sure how or when she died. According to Metropolis, “No record remains as to how or when [Chiyome] met her end, but the fates of her aruki miko were quite likely short and unpleasant.”