Onibi is a type of atmospheric ghost light in legends of Japan. According to folklore, they are the spirits born from the corpses of humans and animals. They are also said to be resentful people that have become fire and appeared. Also, sometimes the words "will-o'-wisp" or "jack-o'-lantern" are translated into Japanese as "onibi".
Outline
According to the Wakan Sansai Zue written in the Edo period, it was a blue light like a pine torchlight, and several onibi would gather together, and humans who come close would have their spirit sucked out. Also, from the illustration in the same Zue, it has been guessed to have a size from about two or three centimeters in diameter to about 20 or 30 centimeters, and to float in the air about one or two meters from the ground. According to Yasumori Negishi, in the essay "Mimibukuro" from the Edo period, in chapter 10 "Onibi no Koto", there was an anecdote about an onibi that appeared above Hakone mountain that split into two and flew around, gathered together again, and furthermore split several times. Nowadays, people have advanced several theories about their appearance and features. ;Appearance ;Number ;Times of frequent appearance ;Places of frequent appearance ;Heat
Types of onibi
As onibi are thought of as a type of atmospheric ghost light, there are ones like the below. Other than these, there is also the shiranui, the koemonbi, the janjanbi, and the tenka among others. There is a theory that the kitsunebi is also a kind of onibi, but there is also the opinion that strictly speaking, they are different from onibi. ; Asobibi ;Igebo ;Inka ;Kazedama ; Sarakazoe ; Sōgenbi ;Hidama ;Wataribisyaku ;Kitsunebi
Considerations
First, considering how the details about onibi from eyewitness testimony do not match each other, onibi can be thought of as a collective term for several kinds of mysterious light phenomenon. Since they frequently appear during days of rain, even though the "bi" is in its name, they have been surmised to be different from simply the flames of combustion, and is a different type of luminescent body. It is especially of note that in the past, these phenomena were not strange. In China in the BC era, it was said that "from the blood of human and animals, phosphorus and oni fire comes". The character 燐 at that time in China could also mean the luminescence of fireflies, triboelectricity, and was not a word that indicated the chemical element "phosphorus". Meanwhile, in Japan, according to the explanation in the "Wakan Sansai Zue", for humans, horses, and cattle die in battle and stain the ground with blood, the onibi are what their spirits turn into after several years and months. One century after the "Wakan Sansai Zue" in the 19th century and afterwards in Japan, as the first to speak of them, they were mentioned in Shūkichi Arai's literary work "Fushigi Benmō", stating, "the corpses of those who are buried have their phosphorus turned into onibi". This interpretation was supported until the 1920s, and dictionaries would state this in the Shōwa period and beyond. Sankyō Kanda, a biologist of luminescent animals, found phosphorus in 1696, and as he knew that human bodies also had this phosphorus, in Japan, the character 燐 was applied to it, and thus it can be guessed that it was mixed in with the hint from China about the relation between onibi and phosphorus. In other words, it could be surmised that when corpses decay, the phosphorus in phosphoric acid would give off light. In this way, many of the onibi would be explained, but there also remain many testimonies that do not match with the theory that of illumination from phosphorus. After that, there is a theory that it is not phosphorus itself, but rather the spontaneous combustion of phosphine, or the theory that it is burning methane produced from the decay of the corpse, and also a theory that hydrogen sulfide is produced from the decay and becomes the source of the onibi, and also ones that would be defined in modern science as a type of plasma. Since they often appear in days of rain, there are scientists that would explain that as Saint Elmo's fire. The physicist Yoshihiko Ōtsuki also advanced the theory that these mysterious fires are caused by plasma. It has also been pointed out that for the lights that would appear far in the middle of darkness, that if they are able to move by suggestion, then there is a possibility that they could simply be related to optical illusion phenomena. Each of these theories has its own merits and demerits, and since the onibi legends themselves are of various kinds, it would be impossible to conclusively explain all of the onibi with a single theory. Furthermore, they are frequently confused with hitodama and kitsunebi, and as there are many different theories to explain them, and since the true nature of these onibi is unknown, there is no real clear distinction between them.
Other
There are also legends that onibi would float about when ghosts appear in Europe, as in Germany on November 2 on All Souls' Night, a great number of onibi can be seen behind the temple in the graveyard. This was seen as proof that a long line of ghosts had come to the temple, and the ghosts of children wore a white undergarment, participating in the line by "Frau Holle ". Since they had appeared in a graveyard, an explanation was given that it was due to the gasses from decomposition as stated previously.
