The essence of Ōmine Zenkibō lies in the structure of rebirth: "an oni turning into a tengu." It is a tale that embodies the heart of Shugendō in a single being. His source lies in the old tales of En no Gyōja and the oni. The oldest extant text depicting En no Ozunu is the Nihon Ryōiki (early Heian), which portrays him as a thaumaturge who flew through the air commanding demons. The Konjaku Monogatarishū, Book 11 carries the tale of En no Gyōja having demons build a bridge across the mountains, showing the fixing of the image of En no Gyōja as one who commands demons. Zenki was originally a violent oni who carried off human children. En no Gyōja captured him with the secret rite of Fudō Myōō and reformed him into an attendant. By one account, En no Gyōja hid the youngest child of the Zenki couple in an iron cauldron and, through the grief of having one's own child taken, brought them to realize the sin of carrying off the children of others. The reformed Zenki and Goki became dharma-protecting oni and supported En no Gyōja's practice. This Zenki, sublimated into a great tengu at the end of long austerities, is Ōmine Zenkibō. This plot, of a violent being turning into a guardian of the Buddhist law, shows most clearly that the dread of a child-snatching tengu and the faith in a tengu who guards people share a single root. The Ōmine on which Zenkibō sits is the holy ground of Shugendō. The Ōmine training ground founded by En no Gyōja, and the Ōmine Okugake-michi registered as World Heritage, is a perilous route that ascetics still tread at the risk of their lives, and Zenkibō was conceived as its guardian. He is chanted as "the band of Zenki of Ōmine" in the Muromachi Noh play Kurama Tengu, and stands among the forty-eight tengu of the Tengu-kyō (some sources give "Nachi Takimoto Zenkibō"). And the heaviest single point of this lore is that the bloodline of Zenki is said to live on into the present. Of the five lodges kept by the five children of Zenki and Goki, only the Onakabō of the Gokijo family remains today, and the present-day Gokijo Yoshiyuki continues to receive the ascetics of the Ōmine Okugake-michi. This genealogy is hard to source explicitly in old documents and is transmitted as the oral lore of the surviving lodge; yet this real continuity—descendants of a reformed oni guarding the path of Shugendō beyond thirteen hundred years—makes Ōmine Zenkibō not a mere legend but a symbol of living faith. Chigiri Kōsai of tengu scholarship, too, placed him within the system of the great tengu of the many mountains.

This edition is not about a single seat on a particular sacred mountain, but a general treatise that thoroughly unravels "what a tengu is" from the history of its iconography and types. The individual traditions of each seat are left to the page of each great tengu. The form of the tengu is not uniform. The first type is the long-nosed tengu—ruddy face and high nose, clad in the ascetic's headcloth (tokin) and the suzukake robe, a feather fan in hand and one-toothed high clogs on the feet. The second is the crow tengu, with a crow's beak and wings, grasping a sword or a vajra staff. The third are the lesser tengu called leaf tengu and wood-chip tengu, held to be weak and numerous kin. Rather than a fixed classification, these reflect the breadth of the tengu image across eras and regions. The iconography shifted over time. The Heian-period tengu was first conceived as a bird like a black kite, and the image of the crow tengu retains that vestige. The long nose grows prominent only from the late Kamakura period; the Zegaibō Emaki depicts a scene in which a tengu that had disguised itself as a human has its nose lengthen as it returns to bird form. As for the origin of the long nose, there are theories that derive it from the high-nosed Jidō mask of gigaku and link the crow tengu to the Karura (Garuda) mask, and a view that sees the long nose as an iconographic vestige of a bird's beak—but none can be called settled doctrine. It was overlaid with the god Sarutahiko, described in the Nihon Shoki as having a nose seven hand-spans long, and the custom arose of using a tengu mask for the role of Sarutahiko in festivals. The tengu's dual nature is rooted in the Buddhist notion of the way of the tengu. Because it studies the Buddhist path it does not fall into hell, and because it handles heterodox arts it cannot reach paradise either—an intermediate state, and the one who falls there was held to be the arrogant monk. The Tengu Zōshi depicts this notion as satire of the monks of the seven great temples, yet Chigiri Kōsai too warns that the simplification "only arrogant monks become tengu" goes too far. Demon though it is, once subdued it turns to guardianship, and it was held that if a Shugendō practitioner recites the Tengu Sutra he may summon the tengu of the various provinces to grant his wishes—this amplitude between guardian and demon is the very core of the tengu. The certain medieval source for the grouping called the "Eight Great Tengu" lies in the libretto of the Muromachi-period Noh play Kurama Tengu. The passage in which the great tengu calls up the tengu of the provinces he commands in geographical order—"In Tsukushi, Buzenbō of Hiko-san; in the four provinces of Shikoku, Sagamibō of Shiramine; Hōkibō of Ōyama; Saburō of Iizuna… the host of Zenki of Ōmine, Takama of Katsuragi"—shows that the Eight Great Tengu were rooted in medieval belief and performing arts, not an Edo invention. Still, the composition wavers by source, with a variant that adds Hōkibō of Ishizuchi-san; it is no fixed roster.

A reconstruction based on Toriyama Sekien’s image and brief note. It appears as a small monk drenched by rain, emerging on rainy nights in the mountains. It softly asks passersby for offerings due to a monk, but refusal does not necessarily bring harm. Its place is tied to the sacred Shugendō ranges of Ōmine and Katsuragi, yet no verified lore links it to specific temples or persons. Later sources that say it begs for food or small coins likely simplify Sekien’s term “sairyō” (offerings), with little direct oral backing. Its wandering is said to occur only on fine-threaded rainy nights, and reports from clear nights or downpours are uncertain. Methods to banish or summon it are unknown, and meetings on mountain paths are told merely as fleeting oddities.