In the history of Japan, ninja (also known as shinobi) operated as spies, assassins, or thieves; they formed their own caste outside the usual feudal social categories such as lords, samurai, and serfs. Ninja often appear as stock characters in Japanese popular culture and in global popular culture.
History
The ninja first entered popular culture in the Edo period. In modern Japan, ninja are a national myth that stems from folk tales and continues through modern day popular culture. Though many Japanese warriors performed amazing feats, there is no evidence that any of them were supernatural. Some of the folk tales are based on historical figures, such as a daimyō (lord) challenging a ninja to prove his worth by stealing his pillow or weapon while he slept.
Legendary abilities
Superhuman or supernatural powers were sometimes associated with the ninja. Such powers include flight, invisibility, shapeshifting, the ability to "split" into multiple bodies, the summoning of animals, and control over the five classical elements. These notions stemmed from popular imagination regarding the ninja's mysterious status, as well as romantic ideas found in later Japanese art during the Edo period. Magical powers were sometimes rooted in the ninja's own efforts to disseminate fanciful information. For example, Nakagawa Shoshujin, the 17th-century founder of Nakagawa-ryū, or martial art style, claimed in his own writings (Okufuji Monogatari) that he had the ability to transform into birds and animals.
Perceived control over the elements may be grounded in real tactics, which were categorized by association with forces of nature. For example, the practice of starting fires in order to cover a ninja's trail falls under katon-no-jutsu ("fire techniques").
The ninja's adaption of kites in espionage and warfare is another subject of legends. Accounts exist of ninja being lifted into the air by kites, where they flew over hostile terrain and descended into or dropped bombs on enemy territory. Kites were indeed used in Japanese warfare, but mostly for the purpose of sending messages and relaying signals. Turnbull suggests that kites lifting a man into midair might have been technically feasible, but states that the use of kites to form a human "hang glider" falls squarely in the realm of fantasy.
Kuji-kiri
Kuji-kiri is an esoteric religious practice which, when performed with an array of specified hand "seals" (kuji-in), or gestures, was meant to allow the ninja to interact with the spirit world and allow them to perform superhuman feats.
The kuji ("nine characters") is a concept originating from Taoism, where it was a string of nine words used in charms and incantations. In China, this tradition mixed with Buddhist beliefs, assigning each of the nine words to a Buddhist deity. The kuji may have arrived in Japan via Buddhism, where it flourished within Shugendō. Here too, each word in the kuji was associated with Buddhist deities, animals from Taoist mythology, and later, Shinto kami. The mudrā, a series of hand symbols representing different Buddhas, was applied to the kuji by Buddhists, possibly through the esoteric Mikkyō teachings. The yamabushi ascetics of Shugendō adopted this practice, using the hand gestures in spiritual, healing, and exorcism rituals.
Later, the use of kuji passed onto certain bujutsu (martial arts) and ninjutsu schools, where it was said to have many purposes. The application of kuji to produce a desired effect was called "cutting" (kiri) the kuji. Intended effects range from physical and mental concentration, to more incredible claims about rendering an opponent immobile, or even the casting of magical spells. These legends were captured in popular culture, which interpreted the kuji-kiri as a precursor to magical acts.