Kappa is a mythical Japanese creature, known for its malicious tendencies:
Their pranks range from the relatively innocent, such as loudly passing gas or looking up women's kimonos, to the more troublesome, such as stealing crops, kidnapping children, or raping women. In fact, small children are one of the gluttonous kappa's favorite meals, though they will eat adults as well. They feed on these hapless victims by sucking out the shirikodama (???, shirikodama?) (or entrails, blood, liver, or "life force", depending on the legend) through the anus (Source: Wiki)
Pink Tentacle has a neat collection of images of Kappa, as drawn in the Edo Period (1603 - 1867). Link - Thanks rtfm!