We know little about the origins of the Ninja, the 'children of darkness' - mysterious shadow-warriors who maintained their eerie mist-shrouded mountain secrecy in the Iga and
Probably closer to the truth, according to Stephen Hayes (the first American to be accepted as a personal student of Masaaki Hatsumi, the thirty-fourth master of Togakure-ryu Ninjutsu) is that these warriors were ex-military men who fled
"They expounded systems of integrated mind-body awareness, based on personal understanding of the order of the universe [and an] unconventional way of looking at situations and accomplishing things... The original Ninja were mystics, in touch with powers that we would describe as psychic today. Their ability to tune into the scheme of totality and thereby become receptive to subtle input from beyond the usual five senses was strange and terrifying..."
Their spirituality or mysticism, however, was not based on empty and impractical religious teachings but on highly advanced combat skills and practical arts of deception and warfare, where warriorship was linked to natural law. Spirituality was not regarded as an external projection onto distant deities, as our religions are in the West, but as a way to inner knowledge, self-mastery and personal power.
To arrive at their understanding, the Ninja developed a comprehensive and holistic map of the human psyche and life cycle, which linked the inner and outer worlds - the world of creativity and imagination and that of time, space and nature - to give a full picture of life and the challenges facing every warrior on his path to liberation and happiness, as well as the means of overcoming these trials. This map revolved around the elements of Fire, Water, Air and Earth, and the qualities of Fear, Power, Clarity and Fatigue. The map can be looked at as offering four gates that we must all step through if we want an authentic spiritual life and one that has meaning for we who we really are. (New Age Info)