In Japan, Tengu are regarded as an existence that belongs to the mountains, while in Chinese legends they are the embodiment of comets and meteors. In Buddhism, Tengu are fallen monks or the final form of the metamorphosis undergone by practitioners of ShugendōWP.
Tengus are a species of Elementals affiliated with parts of nature, such as mountains, skies, wind, or fire. They're very different from Divine Spirits, but if anything, they're closer to Divine Spirit than to humans. Although they normally don't interact with humans, that's not a hard rule, as shown by the examples of Ushiwakamaru and the Kyouhachiryuu disciples. They have a clear precedent of coming in contact with humans and granting them something. They granted knowledge, techniques, Mystery, and secret arts... but that's not the only thing they can grant.
An Usen is a fan made of feathers, usually from hawks or eagles. It's usually a tool used to command troops, but on the other hand, they appear in legends and paintings as tools of Mystery used by Tengus and Xians - tools containing vast amounts of supernatural power. The well-known Tengu fans. Tengu Fans' main effect is to whip up violent winds, but a tengu's fan is also said to possess other abilities, such as creating doubles, granting the owner flight and extremely rapid movement, controlling fire, and exorcising evil.
The ShugendōWP (修験道?) religious sect in Japan is a unique Japanese Magecraft that combines both Religion and Magecraft into a unique blend. It is capable of the Hihatsuhou or Flying Bowl technique, which grants the user the ability to freely move a small metal disc, allowing it to move following an impossible arc and without a sound, and yet with a ferocity that could challenge a wild beast. It is also capable of an ability known as the Raven or Tengu Flight technique, a great leap where as if ignoring gravity itself their body soars unnaturally a few meters into the air. If taken to the extreme, it could be said to be one step short of True Magic, an ability close to spatial teleportation. The Shugenja, practitioners of Shugendō, can also create a special Tengu fire that chars to the bone and even affects people who are normally resistant to fire.
The Myourenji were a school of Shugendō that took corrupting into a tengu and finding one's way to hell as a premise. Myourenji practitioners gain an abhijna after 100 years of training. Learning one out of the six abhijna is enough to make you a tengu. Three of the abhijna are Shinsokutsuu, the power to run long distances; Tashintsuu, the power to read people's minds; and Roshintsuu, awareness of one's life span and predestination. However, the Myourenji school was all slaughtered by its star pupil, Arou Myourenji, out of disgust toward its method of kidnapping children to be students and abandoning the ones who couldn't keep up.
Humans with tengu training
- Kiichi Hougen profile - translated by Comun
- Fate/Grand Order - Event: Little Big Tengu
- Fate/Grand Order — Ushiwakamaru (Assassin) Profile
- Fate/Grand Order material I: section on Ushiwakamaru's Noble Phantasms, translated by mewarmo990 at Beast's Lair.
- Lord El-Melloi II Case Files Volume 1: case. Adra Castle Separation - Chapter 1 Part 4
- Lord El-Melloi II Case Files Volume 1: case. Adra Castle Separation - Chapter 4 Part 1
- Fate/Grand Order: Cosmos in the Lostbelt - Avalon le Fae: Fae Round Table Domain - Chapter 9 Section 4
- Fate/Grand Order - Kijyo Koyo's profile - Translated by Konchew