At the beginning of the academic year, all the pupils in Class 2-D at Kairei Private Middle School receive an email containing a "class hierarchy." Tsubaki Himeyama holds the highest rank and manages to dispel any unease arising from this announcement with her upbeat and lively manner. The class resumes normality until Himeyama's lifeless body is found on school premises. After the funeral, her classmates come across notes addressed to them on their desks - suicide letters left by Himeyama. Could these epistles expose the concealed truths of Class 2-D?