Database: Koyasan

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Kūkai established Kongōbu-ji temple in Koyasan (or Mount Kōya) as a center for ascetic practice when he founded the Shingon school in the early 9th century; although the position as head of the Shingon was taken by Tō-ji and Ninna-ji in the capital, Koyasan was the main temple location in Kii province during the Middle Ages. Most of the main priests at Kongōbu-ji temple were the children of Kii samurai, meaning that establishing good relationships with Koyasan could be useful among the lords to maintain their territories and expand their authority.

Based on the belief that Miroku (or Maitreya) would appear on Mount Kōya 5.6 billion years after the death of Buddha to save the world, many customs emerged as a way to receive Miroku's salvation, including burying sutras, one’s own hair, or the remains of close relatives. These customs spread among the aristocrats of the imperial court from the 11th century and, by the Middle Ages, the belief in Koyasan had become so widespread among the warriors of the shogunate that many pavilions and pagodas were built with their help. In the 16th century, several prominent warlords (such as the Takeda family of Kai, Uesugi clan of Echigo, Hōjō and Satake of Kantō, and Mōri of the west) had established burial sites at Koyasan.

Low-ranking priests known as Koyahijiri spread the Kōya faith among the common people in various regions. However, in 1578, Oda Nobunaga arrested and executed many of these priests, believing that Koyasan was helping Nobunaga's enemies.