The kappa (河童, “river-child”) is an amphibious demon from Japanese folklore, often depicted as a humanoid turtle creature. They are known to drown people in search of the swimmer's shirikodama (尻子玉), a mythical orb located in the anus which is believed to contain the human soul.

Kappas have a divet (called a dish) at the top of their heads. The source of the kappa's power lies in the liquid in this dish. They are very polite, and you can easily spill the dish by bowing, to which they bow back in return.

Here are old and new artist renditions of kappas (including some trying to steal your soul through your ass).