At a prestigious high school in Tokyo, the third grade D Class consists of high scoring students. This is a group with a history, as all of their previous homeroom teachers have been driven crazy within a short period of time and quit. It turns out that the students in D Class enjoy the sport of pushing teachers to the edge, ultimately watching them descend into mental collapse. They are highly skilled at this game and have yet to lose. Then one day, Tsuneo Yoshizawa appears before the D Class as their new homeroom teacher. Tsuneo Yoshizawa keeps a smile on his face no matter what, somehow enduring their relentless verbal and physical attacks. In frustration, the students' behavior gets worse and the situation escalates. Eventually, they find themselves concocting a plan to kill their teacher.