The Master of the Labyrinth (Hangul: 미궁의 주인) is the final boss encountered White Day: A Labyrinth Named School and Remake. In the original game she is a spirit/entity of unknown origin who has the ability to posses body's of other people, while in the remake she is the result of the spirit of Seong-ah feeding off the negative energy and emotions of the school.

In 1999, Eun-mi, Seong-ah's mother, used the music teacher in a ritual that was supposed to revive her daughter, with Na-young.