A woman in a surgical mask — unremarkable in Japan, which is the point — who stops pedestrians, usually children walking home alone, and asks: 'Watashi, kirei?' Am I pretty? Both answers are traps. 'No' is answered immediately; 'yes' is answered with the mask coming down, a mouth slit ear to ear, and the second question: 'Even like this?'
The 1979 flap was serious enough to enter the public record: schools in Gifu, Kanagawa, and Hokkaido organized group walks home, police increased patrols, and at least one prefectural newspaper ran the story straight. Folklorists trace the panic's spread rate along commuter rail lines.
The countermeasures in the folklore are precise and strange: give an ambiguous answer — 'so-so' — which confuses her long enough to walk away; or offer hard candy, which she accepts. Do not run. Every version of the legend agrees she is faster than you.