The Yellow-Bellied Sea Snake: The True Identity of Ryujashin. The true identity of Ryujashin is the yellow-bellied sea snake that inhabits tropical and subtropical open oceans. Due to its black and yellow body color, it was praised as "truthfully manifesting the aspect of Heaven and Earth, Dark and Yellow"^[2]. "Dark and Yellow" refers to the blending of the color of the heavens (dark/black) and the earth (yellow), a phrase praising the mystery of the sky and the eternity of the earth. The seasonal phenomenon of this warm-water sea snake riding the Tsushima Current to wash ashore on the Izumo coast in late autumn overlapped with the belief that deities gather during the Kamiari month, crystallizing into the messenger god faith.

The Kamimukae Ritual and Inasa Beach. On the night of the 10th day of the 10th lunar month, the Kamimukae festival is held at Inasa Beach, the stage of the Kuniyuzuri myth, to welcome the eight million deities arriving from beyond the sea^[1]. At this time, Ryujashin serves as the guide, leading the deities from the beach to Izumo Taisha. The deities lodge at the shrine's Jukusha (nineteen shrines) and are believed to hold the "Kamihakari" (divine assembly) over human affairs and destinies, particularly matchmaking, during the seven-day Kamiari Festival starting on the 11th. Ryujashin is involved in welcoming the gods not only at Izumo Taisha but also at nine other shrines in Izumo, forming the core of the Kamiari faith throughout the region.

Messenger God from the Eternal Land. In ancient Japanese beliefs, deities were thought to either descend from heaven or cross the sea from Tokoyo-no-Kuni (the Eternal Land) or the realm of the sea god^[2]. The sea snakes that arrived punctually with the season were seen exactly as these messenger gods from Tokoyo. This resonates with the otherworld view of Izumo mythology, where Okuninushi departed for Tokoyo-no-Kuni after completing the nation-building with Sukunabikona. Ryujashin, crossing the boundary between the sea and the otherworld, tells the story of Izumo being a sacred place connected to the otherworld beyond the sea since ancient times.

Dedication and Folk Belief: Ryuja-ko. In the Izumo region, there remains a custom of dedicating the washed-ashore sea snakes to Izumo Taisha and enshrining them in household kamidana (Shinto altars)^[2]. Within the Izumo Taishakyo sect, the Ryuja-ko (a lay believer group) was organized to revere Ryujashin as a divine messenger offering protection against fire, water disasters, theft, and bringing good fortune. Talismans of Ryujashin have been distributed to members. Becoming an independent object of worship despite being a divine messenger makes Ryujashin a unique form of faith born from Izumo's Kamiari beliefs.