Sannō Ichijitsu Shintō
Sannō Shintō was a syncretic shinto group with elements from Tendai buddhism of Enryaku-ji Temple. Sannō, or “King of the Mountain”, is a common name of the guardian deity of Tendai Buddhism. The roots of the Shintō-Buddhist amalgamation that developed the belief in Sannō can be traced back to the early Heian period, when Buddhist monks regard a number of Shinto deities as guardian of Buddhism. From the beginning of the Kamakura period, theories of that were formulated. The most important of the syncretic schools to emerge were Sannō and Ryōbu Shintō.
Its early modern doctrines that concern Tōshō-gū are specially distinguished as Sannō Ichijitsu Shintō or Ichijitsu Shintō.
Sannō Shintō no longer exists.
Tendai doctrine allowed Japanese Buddhists to reconcile Buddhist teachings with the native religious beliefs and practices of Japan. In the case of Shinto, the difficulty is the reconciliation of the pantheon of Japanese gods, as well as with the myriad spirits associated with places, shrines or objects, with Buddhist teachings. These gods and spirits were initially seen as local protectors of Buddhism.
Sannō Shintō 山王神道 was a specifically Tendai branch of syncretic Buddhist-Shinto religious practice, which revered kami called the Mountain Kings or Sanno Sansei 山王ニ聖 and was based on Hie Taisha 日吉大社 a shrine on Mount Hiei. The Togakushi Shrine was also associated with the Tendai school before it was separated from Buddhist institutions by the Japanese state during the separation of Shinto from Buddhism in the 19th century.
These religious ideas eventually led to the development of a Japanese current of thought called honji suijaku, which argued that kami are simply local manifestations of the Buddhas. This manifestation of the Buddhas was explained through the classic Mahayana doctrines of skillful means and the Trikaya.
In 1571, Oda Nobunaga attacked Enryaku-ji Temple, and Hie Taisha was burned down along with the Temple.