A kappa is a Japanese mythological water sprite or, literally, "river child" (河童). One of the more popularly known yōkai (Japanese mythological creature) in Japan, kappa are generally green or yellow, have a tortoise-like shell on their backs, a tonsured head, and a fishy smell. Their behaviour ranges from helpful and mischievous to downright malevolent, as they are known to stalk the water's edge and drag unfortunate passers-by into the depths.
This is a companion discussion topic for the original content at https://www.worldhistory.org/kappa/.