The Kappa is a Japanese creature that has the body of a tortoise, the head of a monkey and limbs that are lined with scales. Some believe that the kappa is of Ainu origin, others that it is descended from the monkey messenger of the River god. They are approximately the same size as a ten-year-old child, yellow-green in colour and with an indentation on the top of the head, which is their main distinguishing marks. If the water in the hollow is spilled, that kappa immediately loses its powers. They live in rivers, ponds or lakes and are vampires, feeding on their prey through the anus. Horse and cattle blood satisfies them as well as does human blood.
Kappa are also said to be capable of raping women, a characteristic that they share with the oni. Apart from blood, they have a liking for cucumbers and one way of pleasing them is to throw cucumbers with the names and ages of the family into the water where the Kappa live. They will then not entice these people into their clutches. Another feature of the Kappa is their ability to keep a promise and hold a bargain.
In spite of their many bad habits, they are strangely polite, and if treated with courtesy, this river dwelling creature is harmless. Many times, in order to be polite they bow, and spill the water from their heads. However, if it is ill-treated, it will prey on humans.
Relevance to Inuyasha
Not much, although very famous as far as Japanese demons go, kappa have only appeared once in the series. When Inuyasha is searching for the castle of Tsukomo no Gami he meets two kappa who give him directions. They speak in a kansai dialect.