Each person is graded through a popular vote against the backdrop of a girl's high school and if they receive an F grade, they become legitimate victims of school violence.

Sung Soo-Ji (Bona) is transferred to Baekyeon Girls' High School in Seoul. She begins classes there in grade 2 class 5. On her first day at her new school, she notices her class being generally peaceful, but also a bit weird. She has to participate in a strange vote called the Pyramid Game, where the students in grade 2 class 5 participate. The game is held once a month and it is like a popularity vote, but the student who gets the lowest number of votes gets an "F" and becomes the target of school violence. Sung Soo-Ji gets zero number of votes and becomes the next target. She is bullied by her classmates and nobody seems to care about that in her class. Sung Soo-Ji tries to get out of her predicament and also tries end the Pyramid Game at her school.—AsianWiki