In Japanese folklore, a kappa is a water-dwelling yōkai associated with rivers and ponds, where it may drag people or animals underwater; it is also famously fond of cucumbers. Traditional accounts describe the creature as human-like, green or scaly, web-fingered, and equipped with a turtle-like shell.
A kappa’s most distinctive feature is the dish-shaped depression on its head, which holds water. Folklore says that spilling or drying this water weakens the creature, so bowing can be a useful trick: the kappa may bow back and lose the water from its dish. Stories vary by region, and later versions often make the kappa mischievous rather than purely deadly.
The cucumber connection remains visible in Japanese food culture. Kappamaki is a cucumber-filled sushi roll named for the creature. Kappa legends also explain why the yōkai is commonly linked with sumo wrestling, horse-dragging, and dangerous waterways.