Background
Kuchisake-Onna (or the Slit-Mouthed Woman) is a prominent Japanese urban legend. Rumors of alleged sightings of Kuchisake-onna began spreading in 1979 around the Nagasaki Prefecture, causing panic in many Japanese towns. Reports also indicate that children were dismissed from school in groups escorted by a teacher for safety, and police officers increased their patrols.
Kuchisake-Onna later returned as a vengeful spirit wearing a surgical mask (which isn't uncommon in Japan, as many Japanese people wear surgical masks to prevent other people from being infected by their colds and sickness). She will approach a child and ask them,
"Am I pretty?" If the child answers "Yes.",
she will take off her surgical mask, revealing her Glasgow smile and ask, "How about now?"
Mitsuba is always watching you.
If the child changes their answer to "No", kills them. If the child sticks to their answer of "Yes", she will slit their mouth just like hers. Running away from her will not work, as she will simply reappear in front of the victim. The only sure way of escaping Kuchisake-Onna alive and unharmed is to give her an ambiguous answer such as "You are average" or "so-so" which will confuse her, allowing you to get away.
Also, if you drop candy or fruit, she will become busy looking for it and give the person enough time to escape. If the victim throws sweets and candies at her, she would be distracted and try to eat them. This gives the victim enough time to run. Kuchisake-Onna would also have a privilege to appear in front of the victim.The origin of Kuchisake-Onna begins in a Japanese village. She was the prettiest woman in this village. She would always ask the little children "Am I pretty?" Being the pretty woman she was, the children would always say "Yes!"
One day Kuchisake-Onna thought she could get away with cheating with her husband. So she tried, but she got caught. As revenge, her husband slit her mouth. Soon after, she died, either from her injuries or suicide.
Media
The Slit-Mouthed Woman urban legend has appeared prominently in two Japanese films: Carved (2007) and it's prequel Carved 2: The Scissors Massacre