Oni (鬼, oni lit. Little Demon) are fabulous creatures from Japanese folklore, similar to Western demons or ogres. They are almost always depicted as beings with incredible strength and power; physically, two long horns are said to grow from their heads. The earliest folktales of oni generally described them as benevolent creatures able to ward off evil and punish the wicked. However, over time, oni began to be seen as cruel, malevolent creatures, content only to destroy.
In the Touhou world, oni are generally jolly and love to drink, feast, and compete with humans in any kind of contest, from simple physical fighting to drinking games. Long ago, when an oni found a human that they liked, they tempted that human into challenging them in any way the human desired. Should the human lose, they were abducted. Because normal humans were nowhere near an oni's level of ability, humans resorted to sneaky underhanded tactics in order to beat the oni. Tired of being tricked and killed all the time, the oni swore off humans forever and left for a place beyond human reach, or so the legend says. It was later on revealed in Subterranean Animism that the oni have taken refuge underground.
- Example: Suika Ibuki and Yuugi Hoshiguma