The legend is said to originate with a young woman who lived hundreds of years ago (some versions of the legend state the Heian period) and was either the wife or concubine of a samurai. She is said to have been very beautiful but also very vain, and possibly cheating on her husband. The samurai, extremely jealous and feeling cuckolded, attacked her and slit her mouth from ear to ear, screaming "Who will think you're beautiful now?"

The urban legend picks up from this point, stating that a woman roams around at night (especially during foggy evenings), with her face covered by a surgical mask, which would not be especially unusual, as people with colds often wear masks for the sake of others in Japan. When she encounters someone (primarily children or college students), she will shyly ask, "Am I beautiful?" ("Watashi kirei?"). If the person answers yes, she will take off her mask and say, "Even like this?" At this point, if the victim answers "No," she will slay them or cut their mouths to resmeble hers (in many versions, her weapon is a pair of scissors). If the victim tells her she is pretty a second time, she follows the victim home and slays them at the doorway to their residence, due to the fact that "kirei" (きれい), Japanese for 'pretty,' is a near homophone of "kire" (切れ), the imperative form of "to cut". In other versions of the myth if you reply yes after she removes the mask she will give you a large blood soaked ruby and walk away.