Yamabiko

Yamabiko — once a human student named Kunihiko Yamada — preceded the main cast in crossing over to the otherworld, spending five millennia adrift in solitude. Unable to save the girl he cherished, Kodama, he carried that grief until it reshaped him entirely, leading him to abandon his human form and inhabit the body of a black dog. Calm in demeanor yet weathered by centuries of loss, he steps into the role of guide for Nagara and Mizuho in the story's later chapters, offering hard-won wisdom before quietly bearing witness to their final choice and departure.