Kokū-daiko has no body. The apparition is the sound itself. It is heard most often around June on the beaches and capes of Suō-Ōshima, particularly between the evening change of wind and midnight. Islanders also connect it with the roar of the sea and echoes among the rocks. Natural acoustics and a spiritual event cannot be cleanly separated, making Kokū-daiko a sound apparition rooted in the experience of life on the island. The origin story tells of a boat carrying a troupe of performers that was swallowed by a storm. The people aboard beat their drums fiercely for help but never returned. Ever since, the rhythm has revived over the water in the same season. Some witnesses hear quick, light strokes like a small tension drum; others remember one slow, broad blow like a shrine drum. The sound changes with the listener and has no single fixed rhythm. Some communities avoid calling it an omen of disaster. They press their hands together instead, consoling the spirits beneath the sea. The surviving record gives neither a year for the wreck nor the names of those who died, leaving the story entirely within oral tradition. Yet the drum that seems to retreat when approached and draw near when heard from afar turns an islander's knowledge of echo, weather, and death into a vivid maritime ghost story.