Iga and Kōga clans

The Iga and Kōga clans have come to describe families living in the province of Iga (modern Mie Prefecture) and the adjacent region of Kōka (later written as Kōga), named after a village in what is now Shiga Prefecture. From these regions, villages devoted to the training of ninjas first appeared.^[25] The remoteness and inaccessibility of the surrounding mountains may have had a role in the ninja's secretive development.^[24] Historical documents regarding the ninja's origins in these mountainous regions are considered generally correct.^[26] The chronicle Go Kagami Furoku writes, of the two clans' origins:

"There was a retainer of the family of Kawai Aki-no-kami of Iga, of pre-eminent skill inshinobi, and consequently for generations the name of people from Iga became established. Another tradition grew in Kōga".^[26]

Likewise, a supplement to the Nochi Kagami, a record of the Ashikaga shogunate, confirms the same Iga origin:

"Inside the camp at Magari of the Shogun [Ashikaga] Yoshihisa there were shinobi whose names were famous throughout the land. When Yoshihisa attacked Rokkaku Takayori, the family of Kawai Aki-no-kami of Iga, who served him at Magari, earned considerable merit as shinobi in front of the great army of the Shogun. Since then successive generations of Iga men have been admired. This is the origin of the fame of the men of Iga."^[27]

A distinction is to be made between the ninja from these areas, and commoners or samurai hired as spies or mercenaries. Unlike their counterparts, the Iga and Kōga clans produced professional ninja, specifically trained for their roles.^[21] These professional ninja were actively hired by daimyos between 1485 and 1581,^[21] until Oda Nobunaga invaded Iga province and wiped out the organized clans.^[28]Survivors were forced to flee, some to the mountains of Kii, but others arrived before Tokugawa Ieyasu, where they were well treated.^[29]Some former Iga clan members, including Hattori Hanzō, would later serve as Tokugawa's bodyguards.^[30]

Following the Battle of Okehazama in 1560, Tokugawa employed a group of eighty Kōga ninja, led by Tomo Sukesada. They were tasked to raid an outpost of the Imagawa clan. The account of this assault is given in the Mikawa Go Fudoki, where it was written that Kōga ninja infiltrated the castle, set fire to its towers, and killed the castellan along with two hundred of the garrison.^[31] The Kōga ninjas are said to have played a role in the later Battle of Sekigahara (1600), where several hundred Kōga assisted soldiers under Torii Mototada in the defence of Fushimi Castle.^[32] After Tokugawa's victory at Sekigahara, the Iga acted as guards for the inner compounds of Edo Castle, while the Kōga acted as a police force and assisted in guarding the outer gate.^[30] In 1614, the initial "winter campaign" at the Siege of Osakasaw the ninja in use once again. Miura Yoemon, a ninja in Tokugawa's service, recruited shinobi from the Iga region, and sent ten ninjas intoOsaka Castle in an effort to foster antagonism between enemy commanders.^[33] During the later "summer campaign", these hired ninjas fought alongside regular troops at the Battle of Tennōji.^[33

The plains of Iga, nested in secluded mountains, gave rise to villages specialized in the training of ninjas.