Kaika (yōkai)
Atmospheric ghost lights are lights (or fires) of unknown origin. Examples include the onibi, hitodama and will-o'-wisp. They are often seen in humid climates.
According to legend some lights are wandering spirits of the dead, the work of devils (or yokai), or the pranks of fairies. They are feared by some humans as a portent of death. In other parts of the world, there are folk beliefs that supernatural fires appear where treasure is buried; these fires are said to be the spirits of the treasure or the spirits of humans buried with grave goods. Atmospheric ghost lights are also thought to be related to UFOs.
Some fires of unknown origin (such as St. Elmo's fire or the shiranui) have been explained as optical phenomena of light emitted through electrical activity. Other theories concerning the origin of these fires include the combustion of flammable gases, ball lightning, meteors, torches and other human-made fires, the misperception of human objects, and pranks. Almost all such fires have received such naturalistic explanations.
In addition to the onibi and hitodama, there are other examples of atmospheric ghost lights in legend, such as the kitsunebi and the shiranui:
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