Umibozu is a giant, black, human-shaped yokai that appears before sailors when calm seas suddenly turn turbulent. It usually shows only its upper body, and its size ranges from a few meters to tens of meters.
On emerging it either breaks the ship outright or demands a ladle, then uses it to pour water aboard and drown the crew — so the only escape is to hand it a bottomless ladle and buy time. Its clean, smooth head resembles a monk’s, which gave it the name "sea monk."