Raiju

Raijū (雷獣,"thunder animal" or "thunder beast") is a legendary creature from Japanese mythology. Its body is composed of either lightning or fire and may be in the shape of a cat, tanuki, monkey, or weasel. The form of a white and blue  wolf (or even a wolf wrapped in lightning) is also common. It may also fly about as a ball of lightning or fire (in fact, the creature may be an attempt to explain the phenomenon of ball lightning). Its cry sounds like thunder.
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[Japanese] A Japanese demon whose name means "thunder animal". It is a demon of lightning in the shape of a cat, badger or weasel. During thunderstorms it becomes extremely agitated and leaps from tree to tree. If a tree shows the marks of lightning, people say that Raiju's claws have scratched it open. The demon likes hiding in human navels, so, if afraid, a person should sleep on his or her belly during thunderstorms.