Myth of the sea.

Little is known of the origin of umibōzu but it is a sea-spirit and as such has multiple sightings throughout Japan. Normally, umibōzu appears to sailors on calm seas which quickly turn tumultuous. It either breaks the ship on emergence or demands a bucket or barrel from the sailors and proceeds to drown them. The only safe way to escape an umibōzu is to give it a bottomless barrel and sail away while it is confused.