Raiju

When lightning strikes and splits a tree in half, or tears a hole in a wall, the old Japanese explanation was direct: a creature made of pure electricity fell along with that lightning bolt, and its claws were responsible for the damage. There was a curious warning tied to this legend: never sleep on your back during a storm, because this creature loved to nestle exactly in the navel of anyone sleeping unprotected outdoors.

A creature made of lightning, described as a fox, weasel, cat, badger, or wolf with an electric body, that falls to earth during storms together with the lightning bolts. Restless and swift, it leaps among the trees and can tear apart trunks and buildings struck by lightning.

Within the folk and mythological corpus compiled by the Codex Monstrorum, the creature Raiju occupies a distinctive role in the symbolic imagination of its culture of origin. Its mythos articulates primal human anxieties, the mystery of untamed wilderness, and social norms preserved through the lens of bestiary literature.

It personifies lightning and its effects: the marks on split trees and the fires were ascribed to the raiju's claws. A curious belief holds that it nests in the navel of people sleeping outdoors — hence sleeping prone on stormy days was advised.

On stormy days windows were shut to keep the raiju out — docile when calm but furious and electric when startled by Raijin's thunder. Supposed mummified specimens were displayed in temples and fairs of the Edo period.

First appearance and primary records: The 'thunder beast' of Japanese folklore, companion of Raijin (god of thunder); attested in Edo-period popular tradition and illustrated in prints and yokai encyclopedias of the 17th–19th centuries.

Oral transmissions and preserved manuscripts indicate that legends surrounding Raiju underwent substantive evolution over successive centuries. From archaic oral traditions to classical and medieval written records, each period reframed the creature according to its own ethical and cosmological paradigms.

A variable animal form (fox, weasel, cat, wolf) wreathed in lightning, an electric, crackling body, glowing eyes, sharp claws; it moves in zigzags like the bolt and emits sparks.

It explains lightning, fires, and split trees and ritualizes prudence during storms; it serves Raijin as his beast. It binds the sky, thunder, and the fear of electric fire.

Like the North American thunderbird and the Southern African impundulu, it is an animal of lightning; it stands out for its small-mammal form (fox/weasel), its link to a specific god (Raijin), and the navel belief.

Present in Edo-period art, prints (ukiyo-e), yokai encyclopedias, and pop culture (it inspired electric creatures in games and anime); it is the Japanese personification of lightning par excellence.