In Japanese history, a ninja (忍者) is a warrior, trained in martial arts, and specializing in a variety of unorthodox arts of war. The methods used by ninja included assassination, espionage, stealth, camouflage, specialized weapons, and a vast array of martial arts.
The exact origins are unknown, but their roles may have included sabotage, espionage, scouting and assassination missions as a way to destabilize and cause social chaos in enemy territory or against an opposing ruler, seemingly in the service of their feudal rulers (daimyo, shogun), but in reality as a massive underground organization waging guerilla warfare against the broader imperial system itself.
Ninja as a group first began to be written about in 15th century feudal Japan as martial organizations predominately in the regions of Iga and Koga of central Japan, though the practice of guerrilla warfare and undercover espionage operations goes back much further.
At this time, the conflicts between the clans of daimyo that controlled small regions of land had established guerrilla warfare and assassination as a valuable alternative to frontal assault. Since Bushidō, the samurai code, forbade such tactics as dishonorable, a daimyo could not expect his own troops to perform the tasks required; thus, he had to buy or broker the assistance of ninja to perform selective strikes, espionage, assassination, and infiltration of enemy strongholds.
Ninjutsu did not come into being as a specific well defined art in the first place, and many centuries passed before ninjutsu was established as an independent system of knowledge in its own right. Ninjutsu developed as a highly illegal counter culture to the ruling samurai elite, and for this reason alone, the origins of the art were shrouded by centuries of mystery, concealment, and deliberate confusion of history.
The predecessors of Japan's ninja were so-called rebels favoring mikkyo Buddhism who fled into the mountains near Kyoto as early as the 7th century A.D. to escape religious persecution and death at the hands of imperial forces.
Mikkyō (密教; literally "secret teachings", often translated as "esoteric Buddhism") is a Japanese term that refers to the esoteric Vajrayāna practices of the Shingon Buddhist school and the related practices that make up part of the Tendai school. There are also various Shingon- and Tendai-influenced practices of Shugendō. Mikkyō is a little-understood, yet often sensationalised, synergistic “esoteric construct” that lies at the very core of Japanese spirituality and mysticism.
Mikkyō is a "lineage tradition": meaning that, as well as instruction in the teachings and practices of the tradition, it also involves and requires “‘’kanjo’’ enablements” - initiatorial empowerment-transmissions - from a master of the Mikkyō disciplines.
The collection of teachings and practices that eventually came to be known as Mikkyō had its early beginnings in the esoteric traditions of India and China. As early as the 6th Century, there had begun a major importation of spiritual and cultural ideas into Japan from China. However, it was in the early 9th Century that the formative concepts which would in time become the core of “mainstream” Mikkyo - Shingon and Tendai - were brought to Japan - initially by the monks Kūkai (the founder of Shingon) and Saichō (the founder of Tendai), both of whom had traveled to China to study.
To these initial doctrines & beliefs were later added teachings concerning the powers of mysticism, magic and healing that had gradually begun to reach Japan with the arrival of itinerant monks, priests, hermits and shamanic practitioners, forced for various reasons to flee from China after the fall of the Tang Dynasty.
Blending easily with elements of Shinto practice and the pre-Buddhist folk traditions of ‘’sangaku shinko’’ “spiritual practices connected with sacred mountains”, these imported teachings, combining Chinese Tantric Buddhism, Chinese Yin-Yang magic, Taoism and, at a later date, Tibetan Vajrayāna Buddhism, evolved to become the esoteric Japanese tradition that is Mikkyō.
