Kappa is an aquatic youkai of Japanese folklore. It can be both beneficial and evil and the Japanese believe there are some ways to protect themselves against an evil kappa.
Called "River Child", they live in rivers, lakes and ponds, but never hesitate to climb the mainland in search of their prey. Traditionally the tales portray them as malicious, eager to suck the guts of their victim and drink his blood. They say they especially love the human liver. But they are also represented as intelligent and honorable.

Some say humans learn cure from them, but only by a cost of and amputed arm.