kappa

This is a drawing by a famed Japanese artist Katsushika Hokusai (1815). In this drawing, Hokusai depicted a kappa (河童), a Japanese water imp that lives in ponds and creeks. Its favorite food is cucumbers, which is why a sushi roll with cucumber in the center is called a kappamaki (maki means roll). Its next favorite food is little children. Because of this, signs warning children of the kappa are found next to their dwelling places, and cucumbers are hung from ropes above the water.
When out of water, the kappa depends for strength on the water contained in a shallow dent at the top of its head. Without any water in this bowl-shaped hole, the kappa is helpless. This is why all the children know that one must always remember to bow to the kappa. Polite in spite of its wicked ways, the kappa will invariably bow in return and in doing so lose the water. At this point, it is best not to linger.