At an all girls high school, a strange and disturbing tradition takes place on the last Thursday of every month. On that day, the students of Class 2–5 participate in a secret popularity vote where they rank one another. The results of this vote divide the class into different categories labeled A, B, C, D, and F. While the higher ranks enjoy respect and influence, the students who fall into the lowest category, Grade F, face a far darker reality. Those placed at the bottom are treated as acceptable targets for bullying and harassment, creating a cruel system where fear and social pressure control everyday life in the classroom. As the cycle repeats each month, friendships begin to crack, alliances shift, and hidden tensions grow stronger. Behind the ordinary appearance of school life lies a harsh competition for survival, where students must decide how far they are willing to go to avoid becoming the next victim.