Shiramine Sagamibō is, among the Eight Great Tengu, the tengu most firmly bound to a single person—the Retired Emperor Sutoku. His image cannot stand apart from the story of Sutoku's vengeful spirit.

The Retired Emperor Sutoku, defeated in the Hōgen Rebellion (1156), was exiled to Sanuki and died in the second year of Chōkan (1164) without ever being permitted to return to the capital^[2]. At his place of exile he copied out the five Mahāyāna sutras and sent them to the capital, but, suspected of a curse, had them flung back at him; in fury he swore an oath written in blood and is said to have become, while still living, a great tengu and a great demon (daimaen). Sagamibō guards the Shiramine mausoleum of this Sutoku, whom Yoritomo called "the greatest tengu in Japan." Shiramine-ji is the eighty-first station of the eighty-eight temples of Shikoku, the Shiramine mausoleum is the only imperial tomb in Shikoku, and beside it stands the Tonshō-ji-den, which enshrines the spirit of Sutoku-in.

It was literature that made Sagamibō immortal. Its original source is the mid-Kamakura Senjūshō^[3], attributed to Saigyō, whose "On the New Retired Emperor's Tomb at Shiramine" carries a tale of Saigyō mourning Sutoku's tomb at Shiramine. The Noh play Matsuyama Tengu^[4], which dramatized it, takes Sutoku-in as the shite and Saigyō as the waki, and depicts Sagamibō as a tengu attending Sutoku. Further, the "Shiramine" of Ueda Akinari's Ugetsu Monogatari^[5] is a story in which Saigyō mourns Sutoku's spirit at the Shiramine mausoleum and converses with the wrathful Sutoku-in; Sagamibō became the being running through this lineage since the Senjūshō. The vengeful spirit and the tengu who stays beside it—the relation of Sutoku and Sagamibō is a rare point where the faith in goryō (vengeful spirits) and the faith in tengu meet.

There are two theories on Sagamibō's origin: that it derives from Sagami Ajari Shōson, who sided with Sutoku in the Hōgen Monogatari^[2], and that he was a tengu who came from Mt. Ōyama in Sagami. The latter forms a pair with the seat-transfer tradition arranged by Chigiri Kōsai^[6]—that the Sagamibō of Ōyama, in devotion to Sutoku, removed to Sanuki, and Hōkibō entered the vacant Sagami Ōyama. Either way, Shiramine Sagamibō sits at the western end of the Eight Great Tengu, transmitted at Shiramine in Sanuki as the tengu who keeps guarding the soul of Sutoku, one of Japan's three great vengeful spirits.