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.
Raiju is the companion of Raijin, the Shinto god of lightning. One of its peculiar behaviors is sleeping in human navels. This prompts Raiden to shoot arrows at Raiju to wake the creature up, and thus harms the person in whose belly the demon is resting. Superstitious people therefore often sleep on their stomachs during bad weather.