No-eul has never left her room for three years because of depression and anthropophobia; since their father has to go away for a long time because of work, Ha-neul has to take care of her sister.
Every last Thursday of the month at an all-girls high school, the students of Class 2–5 cast their votes in a popularity poll. The results classify them into Grades A, B, C, D, and F. If they fall into Grade F, they become legitimate victims of school violence.
When mysterious alien spheres start invading the world, high school students are called upon to join the world’s first war against extraterrestrial forces.