Ryōbu Shintō (両部神道), literally “Two-Part Shintō,” is a syncretic system in which Shintō kami worship is thoroughly integrated with esoteric Buddhism, especially the Shingon tradition. The expression “two parts” refers to the central Shingon mandalas—the Womb Realm (Taizōkai) and the Diamond Realm (Kongōkai)—which became the basic framework for understanding and classifying the kami. Within this vision, the cosmos of Shintō is read through the symbolic language of these mandalas, so that the world of the kami and the world of the Buddhas are seen as two aspects of a single sacred reality. This religious synthesis took shape in medieval Japan under the influence of Shingon thought and ritual.

At the heart of Ryōbu Shintō lies the idea that the kami are manifestations or avatars of Buddhist deities, a pattern often described through the honji suijaku paradigm, in which Buddhas and bodhisattvas are regarded as the original ground and the kami as their local appearances. Major Shintō deities were thus identified with particular Buddhist figures from the Shingon pantheon, and shrine traditions were reinterpreted in light of esoteric doctrine. In this way, the familiar landscape of native shrines became a field in which profound Buddhist cosmology was thought to be silently at work, hidden beneath the surface of local cults and myths.

This theological vision was matched by a deep practical and institutional fusion. Buddhist priests served at shrines, and many shrines were closely linked with temples, forming complexes where the boundaries between the two traditions were porous. Buddhist rituals, sutras, mantras, and mandalas were employed in the context of kami worship, and the architecture of sacred sites often blended shrine and temple forms. Over time, this created a religious environment in which ordinary practitioners encountered kami and Buddhas not as rivals, but as interrelated presences within a single, layered sacred order.

Ryōbu Shintō came to shape Japanese religious life for centuries, providing a powerful way to hold together indigenous devotion and imported esoteric philosophy. Although official policies later sought to separate Buddhism and Shintō and dismantle such syncretic forms, the patterns of thought and practice cultivated under Ryōbu Shintō did not simply vanish. They continued to inform how many people understood the relationship between kami and Buddhas, suggesting that the two “parts” of this tradition were never merely doctrinal categories, but living ways of perceiving the sacred woven into the fabric of everyday worship.