The Umibozu is a sea-dwelling yokai from Japanese folklore. Its name is derived from the characters for "sea" and "Buddhist monk", which also alludes to this spirit's possible origins. Supposedly, Umibozu are the vengeful spirits of priests who drowned at sea. Their appearance is that of a giant human head with a shaved scalp and a perpetual smile. They have also been described as having cloudy or mist-shrouded bodies with serpentine limbs.
According to legends, Umibozu capsize ships and drown seamen who insult or disrespect them. According to one story, if angered, they ask that the crews provide a barrel that it proceeds to fill with sea water to drown them. To avoid this disastrous fate, it is necessary to give the Umibozu a bottomless barrel.