Kappas are a fictional sapient species originating in Japanese folklore.
Kappas resemble anthropomorphic turtles the size of a child, with webbed hands and feet and black hair on top of its head. Kappas are fish-eaters but occasionally attempt to pull human beings into the water to devour them or drink their blood. Kappas have a hollow, bald spot on their head which is filled with water from the river it inhabits; if this hollowing is emptied, the Kappa will be paralyzed and might even die.
Kappas are obsessed with politeness and honor, which can be exploited in various ways. The most famous is that a man attacked by a Kappa can bow low to the creature, who will then feel obligated to return the gesture, which will cause it to spill its water and become powerless. Moreover, if the man then refills the paralyzed Kappa's skull with water from its river, the creature will be so grateful that it will obey the man for the rest of his life, or, in other versions, answer all his questions truthfully.
Finally, Kappas, for unknown reasons, find cucumbers even tastier than human flesh, and, if kept supplied in cucumbers, will become harmless to their benefactors, or even help them by bringing them fresh fish or irrigating their fields for them.
Creatures inspired by the folkloric Kappas include: