The raijū (雷獣, "thunder animal" or "lightning beast ") is a yōkai of Japanese mythology. Its name comes from the Japanese words rai (雷, "thunder") and jū (獣, "beast, animal"). His body is composed of light or fire.
He can take the form of a cat, dog, wolf, tanuki (another Japanese mythological creature), monkey, tiger, pangolin, rhinoceros, bat, mongoose, civet, squirrel, rabbit, rat, a tapir, a deer, a marine animal (usually a marine mammal such as a dolphin or a seal), an insect, an arachnid, a cleft palate, a badger, a dragon, a boar, a bear, a porcupine, a leopard, a fox or a weasel.
It can also fly as a ball of light (this creature was created to explain the phenomenon of ball lightning). Its cry is like thunder.
The raijū is the companion of Raiden, the Shinto god of lightning. The demon is usually calm and harmless, however, during storms it becomes very aggressive and destroys fields, trees and homes.
Another strange behavior of this creature is that it sometimes sleeps in the navel of humans. Besides, when the weather is bad, superstitious people systematically sleep on their bellies.