https://www.eurogamer.net/the-folklore-roots-of-sekiros-anus-ball-snatching-enemies
The kappa relate to bums in more ways than one. These yōkai are the source of many an ancient horror tale. Matt tells me they're known to "emerge from the depths to drown swimmers or passer-bys for their shirikodama (literally 'small anus ball')".
"The shirikodama is a mysterious organ said to reside in the human colon, and kappa love to extract them from unwary swimmers the hard way: by hand. Or claw." Matt tells me that in times of old kappa were often blamed for drownings.
