Onihitokuchi

Onihitokuchi (鬼一口) is a Japanese legend where an oni devours a person in a single gulp. The phrase can describe something extremely dangerous or difficult, as well as the swift and effortless handling of a task.

One well-known example appears in the mid-Heian-era work The Tales of Ise (section six, "The Steps of Akutagawa"). In the story, a man had secretly visited a woman for years, but their different social standings kept them apart. One night, he finally eloped with her. As they fled, a thunderstorm forced them to take shelter in a cellar with an unlocked door.

The man placed the woman inside and stood guard outside with his bow and arrow, waiting for dawn. When morning came, he peered in and found the woman gone. An oni living in the cellar had killed and eaten her in one mouthful, and her scream was drowned out by the thunder.

This tale was later illustrated in Toriyama Sekien's yōkai collection Konjaku Hyakki Shūi under the title "onihitokuchi." The accompanying text identified the man as Ariwara no Narihira and the woman as Fujiwara no Takaiko, but The Tales of Ise itself never names them; this identification was a later common interpretation.

Other early setsuwa collections also contain similar stories. In the Nihon Ryōiki (early Heian period), a story tells of a man and woman who made vows to each other one night, but the man was actually a serpent/dragon-like creature that ate the woman—not explicitly an 'oni' in the same sense as later tales. In the Konjaku Monogatarishū (late Heian period), there are multiple tales of supernatural beings abducting and devouring people, but the specific claim that women walking outside at night would be taken by an oni and eaten in one mouthful conflates several different stories rather than summarizing a single canonical account.

One theory suggests that these "onihitokuchi" tales were common because real-life events—wars, disasters, and famines that caused people to die or vanish—were interpreted as oni from another world appearing in this one to carry people away.