Tenka (天火) are a type of kaika told about in various areas of Japan. It is written about in the collection of fantastic stories, the Ehon Hyaku Monogatari from the Edo period and in the essay Kasshi Yawa by Seizan Matsuura and other writings, but it is also told as the folklore of various areas.
In the Atsumi District, Aichi Prefecture, when one's path ahead when on a road at night becomes bright like at noon, it is called a "tenbi" (天火), and in the Ibi District, Gifu Prefecture, the mysterious fires that make a great noise in the evening sky in the summer and fly are called "tenpi" (天火).
In the Higashimatsuura District, Saga Prefecture, the weather would become better once a tenka appears, but the homes that they go in result in someone getting ill, so it is said that they are beaten by a kane and driven out.
In the Tamana District, Kumamoto Prefecture, it is a mysterious fire that would fall from the heavens and has a size about that of a paper lantern, and it is said that a conflagration results when it falls on the roof of a house. In the Saga Prefecture region, they were thought of as a premonition for a conflagration, and were detested.
It is said that tenka were once thought of as a type of vengeful spirit (onryō), and in the document on folk customs "Amakusatō Minzokushi" from the Amakusa islands, Kumamoto Prefecture, there is the following legend. A certain man went to Oniike village (now Amakusa city) to fish, but the villagers treated him as an outsider and treated him ill, and due to that, he died from an illness. From then on, a ball of fire would come flying in Oniike every evening, and it moved on to burn a brush, and without even a chance for the villages to try to extinguish the fire, it spread, and completely burned down the houses of the village. The villagers feared this as the deed of that man's vengeful spirit, and built a jizō at the place where he was ill-treated, and it is said that his spirit is mourned for every winter.
When a tenka flies, there is the theory that it makes a "shan shan" sound like the janjanbi of the Nara Prefecture, and thus it is also called a "shanshanbi." The name "shanshanbi" is told about in the Tosa Province (now Kōchi Prefecture).
According to the "Kasshi Yawa," when the people of Saga find a tenka, if it was left there it would result in their home catching on fire, so they are driven away by gathering around and reciting a Buddhist prayer. By doing that, the tenka would change its direction and flee, at the end when it has been driven all the way to the suburbs, it would disappear in the middle of vegetation.
Also, it is said that tenka could be driven away by fanning them with a setta (a type of sandal), and in the collection of fantastic stories "Fude no Susabi" from the Ansei period, there was one that told about someone in the Hizen Province who lost their home due to a fire and "the fire fell on someone else's home, and the resident of that home used a setta to drive away that fire, resulting in my home catching on fire instead, so I'd like for the residents of that home to pay the expenses for a new home," and implored for a settlement from the daikan (administrators of the Edo peiod).
In the collection of fantastic stories "Ehon Hyaku Monogatari" from the Edo period, it was written about as "tenka" (天火), and according to this, there are those here and there who die by fire when their homes catch one fire. According fantastic story from this same piece of writing, there was a heartless daikan at a certain place, and due to his selfish desires, he ill-treated his subordinates, and got a bad reputation even among his superiors, and when he came down from his seat of daikan next month, a fire came from somewhere that should have had no trace of fire at all burned his house, and he also died from the fire, and all the gold and silver, treasures, and clothing turned to smoke in a flash. When this fire occurred, it is said that someone witnessed the sight of a lump of fire falling from the sky.
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- いずれも原典には「天火」の名がないが、天草のものは後掲『竹原春泉 絵本百物語 桃山人夜話』で、『筆のすさび』のものは『妖怪事典』(ISBN 978-4-620-31428-0)で天火と解釈されている。
- 岩井宏實 (2000). 暮しの中の妖怪たち. 河出文庫. 河出書房新社. pp. 102–103頁. ISBN 978-4-309-47396-3.
- 山口敏太郎. "ハザマトシユキの「お化け大好き」（第5回）". ホラーアリス妖怪王（山口敏太郎公式サイト）. Retrieved 2008-07-09.
- 松浦静山 (2008). "甲子夜話". In 柴田宵曲編. 奇談異聞辞典. ちくま学芸文庫. 筑摩書房. pp. 558–559頁. ISBN 978-4-480-09162-8.
- 菅茶山 (1975). "筆のすさび". In 早川純三郎他編纂. 日本随筆大成. 第1期 1. 吉川弘文館. pp. 85頁. ISBN 978-4-642-08555-7.
- 多田克己編 (1997). 竹原春泉 絵本百物語 桃山人夜話. 国書刊行会. pp. 91頁. ISBN 978-4-336-03948-4.