According to Japanese folklore, when a crab or a shrimp reaches a very old age, it can change into a yōkai called a kebō. Kebō are crustacean-like creatures about the size of a four or five year old child. They have a human-like torso and a bald head, with a face that resembles a crab’s shell. Their lower body is covered with a thick skirt of hair. They have six limbs. Each of their four legs ends in a black-tipped claw-like appendage, and each arm ends in two such claws.

Like crabs and shrimp, kebō live near the edges of bodies of water. They feed upon small fish. Although they have human-like faces, they cannot speak. They do, however, smile and laugh when they see humans.

A picture and description of a kebō are recorded in Shokoku yōkai zukan, a picture scroll from the middle of the Edo period featuring a number of illustrated yōkai with descriptions. This is the only known document detailing this yōkai. According to the scroll, the kebō was sighted in Satsuma Domain, in present-day Kagoshima Prefecture.