Imagine this: a winding river in Japan. The scenery is lovely, the day warm, and all of a sudden something near the water moves. It looks like a child, so you draw closer. But when it turns around you find yourself face to beak with a grinning kappa.
Kappa are a type of water spirit who are considered incredibly intelligent and lecherous creatures, inhabiting bodies of water all throughout Japan. In fact, there are still signs in certain areas warning people of the kappa who are said to dwell in that body of water. They are typically described as being about the size of a 10-year-old child, yellow-green in color, and looking like a scaled monkey or having a tortoise shell instead of skin. They are also said to have beaks on their faces and speak many languages as well. On the tops of their heads is an indentation filled with water that give the kappa their powers, and if they should lose that water they are rendered powerless.
They are known for drowning or devouring children who wander too near the water, waiting in toilets and assaulting women, and occasionally attacking men. However, if you can trick one into bowing, emptying the contents of its head, and offer to replenish it, the Kappa will be generous and grant the person a wish or a favor. They are also attributed to introducing the art of bone setting and salve creating to humans.
Though the benefits to helping one seem great, the majority of signs point away from the kappa, warning people from their habitats. One thing is for certain: if you happen to find yourself face to face with one, bow low and wait for your opportunity to flee, or refill his head and be blessed with any wish you could desire.
For more reading on the kappa (sources):