A kappa—also known as kawatarō, komahiki, with a boss called kawatora or suiko—is a reptiloid kami with similarities to yōkai found in traditional Japanese folklore. Kappa can become harmful when they are not respected as gods. They are typically depicted as green, human-like beings with webbed hands and feet and turtle-like carapaces on their backs. A depression on its head, called its "dish" (sara), retains water, and if this is damaged or its liquid is lost (either through spilling or drying up), the kappa is severely weakened.
The kappa are known to favor cucumbers and love to engage in sumo wrestling. They are often accused of assaulting humans in water and removing a mythical organ called the shirikodama from their victim's anus.
The name kappa is a contraction of the words kawa (river) and wappa, a variant form of 童 warawa (also warabe) "child". Another translation of kappa is "water sprites". The kappa are also known regionally by at least eighty other names such as kawappa, kawako, kawatarō, gawappa, kōgo, suitengu.
It is also called kawauso 'otter', dangame 'soft-shelled turtle', and enkō 'monkey', suggesting it outwardly resembles these animals. The name komahiki or "steed-puller" alludes to its reputed penchant to drag away horses.
The kappa has been known as kawako in Izumo (Shimane Prefecture) where Lafcadio Hearn was based, and gatarō was the familiar name of it to folklorist Kunio Yanagita from Hyōgo Prefecture.
Kappa are said to be roughly humanoid in form and about the size of a child, inhabiting the ponds and rivers of Japan. Clumsy on land, they are at home in the water, and thrive during the warm months. They are typically greenish in color (or yellow-blue), and either scaly or slimy skinned, with webbed hands and feet, and a turtle-like carapace on their back. Inhuman traits include three anuses that allow them to pass three times as much gas as humans. Despite their small stature they are physically stronger than a grown man.
The kappa are sometimes said to smell like fish, and they can swim like them.