Murasaki Kagami, or "Purple Mirror" is an urban legend from Japan as well as a potential supernatural entity of the same name, the exact origins of the urban legend is unknown but it has been referenced in several pop-culture pieces since its creation.
History[]
Mirrors have often been seen as ways for spirit and human worlds to merge and thus the idea of ghosts or other strange creatures inhabiting mirrors is as ancient as mirrors themselves, however the legend of Murasaki Kagami is often stated to be an urban legend, likely based upon much older folklore.
In the legend a young girl finds a mirror and paints it purple only to fall under a curse, by the time she reaches 20 the curse claimed her life and ever since then young girls have become vulnerable to a similar curse where they will befall a great tragedy or death if they fail to forget the phrase "Purple Mirror" by the time they reach 20.