Tengubi

Tengubi (Japanese: 天狗火 or てんぐび, meaning "Tengu fire") is a fireball phenomenon seen near rivers in Aichi, Shizuoka, Yamanashi, and Kanagawa Prefectures in Japanese mythology.

It is also known as tengu no gyorō or taimatsu maru.

It is similar to the kitsune's kitsunebi.

Myths & Legends
Tengubi descends at night from the mountains to the rivers. Often it starts as a small number of fireballs which split into hundreds of smaller flames. These flames hover above the water for some time, as if dancing. Afterwards, they return to the mountains.

In most cases, humans who witness tengubi invariably meet with disaster—usually in the form of a serious illness contracted shortly after the encounter. Because of this, locals who lives in areas where tengubi is common greatly fear this phenomenon. If a local happens to see a tengubi, they will immediately drop prone and hide. Oftentimes they will cover their heads with their shoes or sandals.

Occasionally, tengubi can he helpful to humans. During times of drought, it was common for rice farmers to secretly steal water from their neighbors by redirecting water from the canals into their own fields during the night. This caused a great deal of conflict among the people involved. However, when tengubi appeared above the canals, would-be thieves were thwarted—either out of guilty consciences or because the light from the tengubi made it impossible to sneak around.

Appearance
It appears as one or more (up to several hundred) reddish flames which float about in the sky. These supernatural fires are said to be created by tengu.

Villager Who Provoked the Tengu
Long ago, tengubi was frequently seen in the villages of Kasugai City, Aichi Prefecture. One night, a villager was caught out in the mountains in a sudden thunderstorm. It was cold, and too dark to find his way back home, so he took shelter under a tree and shivered. Before long, mysterious fires began appearing around him. Not only did they warm his chilled body up, but they provided enough light for him to find the road and make it safely back to his village.

It was a common superstition in that village not to go outside of your home on nights when tengubi appeared. If you did, it was said that you would be spirited away into the mountains. One night a particularly foolhardy young man defied the superstition. He walked out of his house, faced the tengubi, and called out, “If you can take me, come and get me!” Suddenly, a large black shape appeared out of nowhere and grabbed the young man. It picked him up and flew away into the mountains. The young man was never seen again.

Origins
Tengubi is created by kawa tengu—”river tengu” who prefer the riversides over the deep mountain valleys where tengu normally live. It is used by these tengu to catch fish at night. For this reason it is also known as tengu no gyorō (“tengu fishing”).

Toriyama Sekien included this phenomenon in his book  Hyakki tsurezure bukuro  under the name taimatsu maru ( taimatsu  meaning “torch,” and  maru  being a popular suffix for boys’ names). He described it not as a tool for tengu to help with fishing, but as a way for them to hinder and interfere with the religious practices of ascetic monks.