The legend of these supernatural beings went back to Japan in the 6th and 7th century. Definitely devilish at their origin, famous for setting forests on fire, kidnapping children, or endlessly tormenting Buddhist monks, the Tengu is a being capable of making a difference between Good and Evil; in turn merciless and terrible or filled with kindness, depending on the travelerís soul who encountered it on a forest path, it meant hell or the last resort for the lost or the reckless who knew his moment of truth had arrived when he suddenly heard mocking fits of laughter above him in the branches.
Half-man ( body), half-bird ( head) the most ancient ones made them look like crows (Karasu Tengu), but the most common ones were those of "little Tengu" (Ko Tengu ) with wings, or the ones of long-nosed Tengu ( Konsha Tengu ). There was in fact a hierarchy that ranked the human-faced Tengu with long nose above those with wings. The Lord of these mountain spirits is Sojobo, represented with a long nose and long white hair. Its power was symbolized by a fan made of seven feathers.
A Tengu may assume a human appearance (child, woman, old man) to better deceive, or appear also under the disguise of a badger (Tanuki) or a fox (Kitsune). But its shadow always betrayed its true nature. The Tengu is credited with an unusual sense of humor, and its mischief was only equal to its arrogance. Tengu are very curious and they are all very knowledgeable about almost everything. A Tengu speaks without moving its lips or its beak. In fact, it uses telepathy to communicate. Also the tengu is known as an anthropomorphic, a shape shifter, which may be reason why there is some confusion to the question about the tengu appearance.
A Tengu may only be defeated by a superior magical power. If he has done many good deeds, a tengu can be reborn as a normal human, the goal of every tengu spirit, especially Sojobo the Tengu King..
Humans can through specific ritual draw the spirit of a tengu into themselves and transform into a creature of incredible power. Ancient Yamabushi were credited with being able to open them selves to the power of a tengu, usually a lesser tengu, but it granted them extra-ordinary skills in martial arts and supernatural powers.
During the 14th century, the tengu began to trouble the world outside of the Buddhist clergy, and like their ominous ancestors the tiāngou, the tengu became creatures associated with war. Legends eventually ascribed to them great knowledge in the art of skilled combat.
This reputation seems to have its origins in a legend surrounding the famous warrior Minamoto no Yoshitsune. When Yoshitsune was a young boy going by the name of Ushiwaka-maru, his father, Yoshitomo, was assassinated by the Taira clan. Taira no Kiyomori, head of the Taira, allowed the child to survive on the grounds that he be exiled to the temple on Mount Kurama and become a monk. But one day in the Sōjō-ga-dani Valley, Ushiwaka encountered the mountain's tengu, Sōjōbō. This spirit taught the boy the art of swordsmanship so that he might bring vengeance on the Taira.
Originally the actions of this tengu were portrayed as another attempt by demons to throw the world into chaos and war, but as Yoshitsune's renown as a legendary warrior increased, his monstrous teacher came to be depicted in a much more sympathetic and honorable light. In one of the most famous renditions of the story, the Noh play Kurama Tengu, Ushiwaka is the only person from his temple who does not give up an outing in disgust at the sight of a strange yamabushi. Sōjōbō thus befriends the boy and teaches him out of sympathy for his plight.
Two stories from the 19th century continue this theme: In the Sōzan Chomon Kishū, a boy is carried off by a tengu and spends three years with the creature. He comes home with a magic gun that never misses a shot. A story from Inaba Province, related by Inoue Enryō, tells of a girl with poor manual dexterity who is suddenly possessed by a tengu. The spirit wishes to rekindle the declining art of swordsmanship in the world. Soon a young samurai appears to whom the tengu has appeared in a dream, and the possessed girl instructs him as an expert swordsman. Some rumors surrounding the ninja indicate that they were also instructed by the tengu.