Kuchisake-onna (口裂け女 Kuchisakeonna ) ("Slit-Mouth Woman") refers to both a story in Japanese mythology, as well as a modern version of the tale of a woman, mutilated by a jealous husband, and returned as a malicious spirit bent on committing the same acts done to her.
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, "Am I beautiful now?" ("Kore demo?"). At this point, if the victim answers "No," she will slay them or cut their mouths to resemble 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. Another version says that if you reply yes, she will take her scissors and cut your mouth from ear to ear, making you resemble her. On most versions of the myth she is impossible to escape, as she can either appear in front of you no matter which way you turn or can move at superhuman speeds and catch you.<Yokai Attack, Kodansha Publishing>
During the seventies, the urban legend went that if the victim answers "You're average", they are saved. When the urban legend was revived around 2000, the answer that would save you was changed to "so-so," with the change that this answer causes the kuchisake-onna to think about what to do, and her victim can escape while she is in thought. Another way to escape while the Kuchisake-Onna is distracted is to throw candy or other sweets at her, or simply offer her candy. One other way is to ask her if you are pretty. She will get confused and leave.
A number of variations are available possibly due to wide spread of part the rumor with people not knowing the whole story. A variation tells of the reason of the slit being made by an unlicensed plastic surgeon, another tells of it being a curse from the excessive use of the power of the inugami from family traditions. Additionally, a modern Kuchisake-onna drives a red sportscar and dresses fashionably.<Yokai Attack, Kodansha Publishing>
During the spring and summer of 1979, rumors abounded throughout Japan about sightings of the Kuchisake-onna having hunted down children.
In October 2007, a coroner found some old records from the late 1970s about a woman who was chasing little children, but was hit by a car, and died shortly after. Her mouth was ripped from ear to ear. It is believed that she caused the panics around that time.
In 2004, a similar legend spread throughout cities in South Korea of a red masked woman, though this may have been fueled by tales of the 1979 cases in Japan, as well as a 1996 Japanese film (see below).
The 1996 film Kuchisake-onna gives the legend a modern origin as the result of a plastic surgery gone horribly awry. Many anime series refer to the legend as well, often in throwaway lines. This is especially true for anime made in the 1980s, when the 1979 reports were fresh in people's memories.
The video game Revelations: Persona has an enemy called Kuchisake-Onna appear when the player first attempts to enter the Castle. Arguably one of the most difficult enemies to kill or negotiate with in the game because they never react with interest (the mood required to obtain a spell card) by any means necessary.
Several kuchisake-onna appear in the manga and anime series Hell Teacher Nūbē.
An episode of the anime Ghost Stories featuring the character was initially scheduled to air on November 5, 2000, but the episode was discontinued when many people complained to Fuji TV because they thought the facial feature looked like cleft palate. 
There is also another Japanese film adaptation, "Kuchisake Onna" directed by Kôji Shiraishi, released 17 March 2007 in Japan that deals with the slit-mouthed spirit seeking victims with a pair of scissors.
Kuchisake-Onna was also the basis for a pink film's plot of the same name.
There is a novel written by Romy Ashby called "The Cutmouth Lady" which refers to a woman with a surgical mask who scares children.
In an omake strip, Caerula Sanguis admits that she used to stand on street corners in Japan and ask children if she was pretty.
In the TVTokyo series Guren Onna, the first villain that Nabekura faces is similar to Kuchisake-onna, but turns out to be a young man.
In the manga series Uwasaya, the Kuchisake-onna is referenced as an urban legend (page 17 of chapter 1).
At the end of an episode of the anime Sayonara Zetsubo Sensei, one of the classmembers (Chiri-chan) takes on characteristics of a Kuchisake-onna, including odd razor-sharp teeth, an exaggerated smile, and carrying a knife.
The film Ringu references her as a similar urban legend to that of the dangerous videotape central to the movie.
In the film the Dark Knight, the villain the Joker has a similar facial disfigurement, with various stories as to the source of the scars.