The temple's name comes from the mountain's shape, which resembles the armor (甲) of Bishamonten. A statue of this warrior deity still sits in the cave where the temple originally began 1,200 years ago.

Koyama-ji是四国八十八所灵场第74番札所,是遍路朝圣者的必经之地。

Kobo Daishi prayed at the Bishamonten cave for the safe completion of Manno-ike Reservoir renovations. The project finished in just three months, and this temple was built to commemorate that achievement.

Koyama-ji供奉药师如来,即药师佛,作为本寺的主尊。