At one high school, a ranking list was sent to Class 2-D, clearly showing the positions of all 24 students and their teacher, creating a hierarchy. Tsubaki, ranked first, is kind, popular, and recognized as the model student. However, one day, she unexpectedly commits suicide.

Days later, each classmate receives a farewell letter from Tsubaki. From that day on, they begin revealing the letters one by one, and the class starts to fall apart. What awaits the students in the end..!?