"Assassination Classroom" Season 3
After going through grueling lessons and tough training under the infamous Koro-sensei, Class E makes the unanimous decision to kill their teacher. In "Assassination Classroom" season 2 finale, Koro-sensei lost much of his power after going head to head with the Reaper and Yanasigawa. With their teacher's current state, every student in Class E performs the mission that they have all been training for -- kill Koro-sensei to prevent the earth from being destroyed. Everyone holds down their teacher and right after his final roll call, Nagisa deals the killing blow.