The Kappa is a Japanese water creature dwelling in rivers and ponds, marked by a turtle-like shell, webbed limbs, and a hollow dish on the crown of its head. It is widely told to lose its strength if the water in that dish dries up.
Alongside tales of dragging children underwater or harming livestock, it is also said to keep its promises when shown courtesy. It figures the fear of drowning at the water’s edge — a familiar yet dangerous boundary.