According to Japanese folklore, Korōri are chimerical beasts made up of parts of the three animals in their name: tiger, wolf, and tanuki. They have the general appearance of a tanuki, with the stripes of a tiger, and the ferocious maw of a wolf. In the late 19th century they were said to be responsible for spreading cholera in Japan.

Korōri take up residence in human houses and infect the people living there with cholera. They can occasionally be seen fleeing the homes after the residents have recovered. They have also been seen feeding on the corpses of those who have succumbed to the sickness.

During the late Edo and early Meiji Periods a number of cholera outbreaks struck Japan. These epidemics killed hundreds of thousand of people, and created an atmosphere of fear and unease. Because of the microbes responsible for cholera are invisible to the naked eye, most people believed that cholera was the work of yōkai. It was sometimes blamed on kitsunetsuki — fox possession — performed by a type of kitsune called an osaki. Eventually it was said to be the world of a brand new a href="/yokai/en" title="Yōkai">yōkai which had never been seen before.

The Edo Period name for cholera in Japan was korori. Various combinations of kanji have been used to write those sounds. One spelling used the kanji for tiger (虎 ko), wolf (狼 rō), and tanuki (狸 ri). This spelling elicited a new creature combining the shapes of those three animals. An 1877 article the popular newspaper Kanayomi printed an illustration and description of the new beast. The story contained a disclaimer that korōri was not a real animal, but an imaginary representation of how fearsome the disease was. In other words, korōri’s real identity is the fear of cholera, rather than the disease itself.

There were a number of korōri sightings during the 1862 cholera outbreak in Edo. A samurai was recovering from the disease when he witnessed a strange beast resembling a weasel lurking about his home. He grabbed a piece of firewood and beat it to death. He roasted the animal and ate it. Later, in the same village, other families with cholera infections began to notice a similar animal lurking around their homes. More and more sightings of these strange beasts were reported. They were even spotted emerging from the bodies of dead cholera victims.