Natori Sanjurō Masatake (born around the 1630's) was a samurai, a teacher of military strategy, and an exponent of shinobi no jutsu. He is most noted for having written the Shōninki, a shinobi manual, and for founding the Kishū-Ryū school of military arts. Natori went by a number of names during his life, including Natori Masazumi, Fujinosshuishi Masatake and Fujibayashi Masatake. His date of death is uncertain, but has been given in some sources as 1708.

Natori was a samurai of the Kii branch of the Tokugawa clan, a house which was directly related to the shogun. His family joined the clan in 1654, and his father, Natori Masatomi, served under Tokugawa Yorinobu as the head of undercover military operations. Masatake was originally employed as a page, probably with the help of his brother, but on reaching adulthood became a foot soldier for the clan. While he was a page the Keian Uprising occured (慶安事件 Keian Jiken). It was a failed coup d'état attempt carried out against the Tokugawa shogunate of Japan in 1651, by a number of rōnin. Sekiguchi Yarokuemon Ujimune, founder of Sekiguchi-ryu, gave up his position as Samurai and became a paid guest in the Kishu Tokugawa clan

His elder brother had inherited his father's position, but despite this Masatake rose through the ranks to the position of ogaban, a senior retainer, and becomes the third grand master of Natori-ryu. Natori studied Kusunoki-ryu and combined it with Natori-ryu. He was payed 25 koku (years worth of rice), while his brother was payed 200-50 koku. His scrolls were widespread by the 1670's and he had regular private meetings with his lord. Natori's lord urges him to change his school's name to Shin-Kusonoki-ryu while around this time he had written three shinobi scrolls, the last one being the Shoninki (true shinobi account) published in 1681-2. In this work, he set down his thoughts on the role and techniques of the shinobi, and the teachings of his family's military arts, focusing primarily on moral character. His lord retires and a new one takes over while he was writing his shinobi documents and, thus, he retired to a place called Ono to continue his studies.