A demon dwarf of Japanese waters, resembling a grotesque little naked man with a tortoiseshell on his back and clawed webbed fingers and toes. He has a greenish skin, round eyes, a beaked nose, and smells strongly of rotten fish. On the crown of his head there is a circular depression filled with water.

The kappa's ancestors are the ghosts of people drowned in Japanese rivers, but this semi-human connection does not endow him with pity for living mortals. He lies in wait for people and other animals straying close to the water's edge, drags them into the water, and consumes them from the inside out.

There are, however, two ways to avoid the clutches of a kappa. One is to watch the water carefully for his appearance, and to give him a polite bow when he surfaces. He will return the bow, the water will pour out of the depression in his head, and he is powerless until he has refilled the depression by submergin again. This process gives the human enough time to escape.

The other method is to carve one's name and age in the skin of a cucumber and throw it into the water. Apparently the kappa is fond of cucumbers, and when he eats the gift he will remember the donor's name and spare him from his clutches.