Kotoshironushi is a Shinto kami encountered as the protagonists gather offerings for the divine feast at Izumo-taisha Shrine. The son of Ōkuninushi, Izumo's supreme deity, he is associated with fishing, maritime safety, and commerce. Mythological tradition recounts his agreement to relinquish control of the land to the heavenly deities by surrendering his spear, contrasting with his resistant brother Takeminakata.

His key interaction occurs when the protagonists seek his offering at Miho Shrine in Matsue. There, he provides a large sea bream (tai), symbolizing his ties to the sea and fishing. The protagonists store this offering within their magic gourd for delivery to Izumo-taisha.

Syncretized with Ebisu of the Seven Lucky Gods, Kotoshironushi is revered for ensuring maritime safety, bountiful harvests, and family prosperity. He shares dual worship with the harvest goddess Mihotsu-hime at Miho Shrine, reflecting its focus on sustenance and abundance. Annual rituals such as the Morotabune Shinji reenact his mythological surrender through boat races and purification ceremonies. His portrayal remains consistent as a cooperative deity supporting the protagonists' quest, rooted in mythological tradition.