The origins of Ono-ji dissolve into myth. Temple tradition holds that the semi-legendary founder of Shugendo, En no Gyoja, established the site in 681, deep in the mountainous interior of what is now Uda, Nara Prefecture. In 824, the great Shingon master Kukai is said to have reconstructed the temple and renamed it Jison-in Miroku-ji. Whether these founding legends are historical fact or devotional embellishment, the temple's connections to the powerful Kofuku-ji in Nara are well documented. Monks from Kofuku-ji were involved in carving the rock-face Buddhist images, and the nearby temple of Muro-ji -- originally a Hosso sect institution -- shared the same scholarly lineage. Ono-ji sits at the western gateway to Muro-ji, nestled in the green mountains where the Kintetsu Osaka Line traces the Uda River valley, just a five-minute walk from Muroguchi-Ono Station. For centuries, pilgrims passed through here on their way deeper into the mountains, pausing at the cliff face before continuing east.

In 1207, the monk Gaen of Kofuku-ji commissioned the great rock carving that would become Ono-ji's defining feature. The cliff on the opposite bank of the Uda River was chosen -- a massive natural wall roughly 30 meters high. Workers carved the rock into a halo shape spanning 13.8 meters in height, then smoothed the interior surface and sculpted a bas-relief image of Miroku Bosatsu, the Future Buddha. The stonemason responsible is believed to have traveled to Japan from Song China, bringing continental techniques to shape Japanese stone. The work was modeled after an even larger Miroku statue on Mount Kasagi in Yamashiro Province, of which only the halo outline survives today. Two years after work began, in 1209, the eye-opening ceremony was held -- the ritual moment when a Buddhist image is considered to come alive -- and the cloistered Emperor Go-Toba himself attended. To the lower left of the main figure, a mandala circle was carved with Vairocana at its center, surrounded by Siddham script characters representing various Buddhas, believed to date from the same period.

When archaeologists surveyed the cliff carving in 1916, they discovered something unexpected. The Miroku figure had a hole in its chest, sealed with a small stone lid just eight centimeters across and three centimeters thick. Inside was a tiny scroll, but exposure and centuries of moisture had rendered its characters illegible. A second cavity was found in the abdomen near the navel, containing another scroll in even worse condition -- so badly decomposed it could not be read at all. Whatever prayers, dedicatory texts, or sacred formulas the 13th-century craftsmen sealed inside their creation remain unknown. The practice of embedding relics and texts within Buddhist statuary was common, but finding such caches in cliff-carved stone is rare. These sealed chambers turned the entire rock face into something more than a sculpture -- it became a reliquary, a container for the sacred hidden within the mountain itself.

In 1900, fire consumed every building at Ono-ji. Ancient records, temple histories, and administrative documents burned to ash. The honzon statue and several other Buddha images were rescued from the flames -- among them a standing figure from the early Kamakura period, crafted in the yosegi-zukuri joined-wood technique, standing 98.8 centimeters tall and now designated an Important Cultural Property. The temple buildings visible today are entirely modern reconstructions. But across the river, the cliff carving faced a different threat: water. Groundwater seeping through the bedrock was eroding the stone surface, encouraging moss growth that obscured the carved features. Between 1993 and 1999, conservators undertook a careful restoration -- removing moss, redirecting groundwater flow paths through the rock, and stabilizing the cliff face. The carving had survived eight centuries of weather. It was designated a National Historic Site in 1934. In spring, weeping sakura trees bloom along the temple approach, their pink petals drifting past the ancient stone face that still watches the Uda River below.