Kappa is a reptiloid kami with similarities to yokai found in traditional Japanese folklore. Kappacan become harmful when they are not respected as gods. They are typically depicted as green, human-like beings with webbed hands and feet and turtle-like carapaces on their backs.
Once befriended, kappa may perform any number of tasks for human beings, such as helping farmers irrigate their land. Sometimes, they bring fresh fish, which is regarded as a mark of good fortune for the family that receives it. They are also highly knowledgeable about medicine, and legend states that they taught the art of bone setting to human beings.
One peculiar trait is that it has a cavity on its head called a sara that retains water or some sort of liquid, which is regarded as the source of the kappa's power or life force. This cavity must be full whenever a kappa is away from the water; if it ever dries out, or if its water is spilled, kappa loses its power and may even die. The kappa are sometimes said to smell like fish and they can swim like them.
Folk beliefs claim the cucumber as their traditional favorite meal. At festivals, offerings of cucumber are frequently made to the kappa. Sometimes the kappa is said to have other favorite foods, such as the Japanese eggplant, soba, natto or kabocha.
In Edo (old Tokyo), there used to be a tradition where people would write the names of their family members on cucumbers and send them afloat into the streams to mollify the kappa, to prevent the family from coming to harm in the streams. In some regions, it was customary to eat cucumbers before swimming as protection, but in others it was believed that this act would guarantee an attack.
