Koyama-ji è associato a Yakushi Nyorai, il Buddha della Medicina, qui venerato come divinità principale del tempio.

Koyama-ji si trova a Zentsuji, nella prefettura di Kagawa, collegandolo a una delle città di pellegrinaggio più note di Shikoku.

Young Kobo Daishi played in this area as a child, building mud Buddha statues and plant temples. The field where he played was called Sen-yugahara (Field Where Hermits Play).

A saint appeared from a cave on Mt. Koyama and told Kobo Daishi to build a temple there. That cave, located to the left of the Daishido Hall, became the birthplace of Koyamaji Temple.