Assassination Time.A tentacled creature of unknown origin destroys over seventy percent of the moon, and he announces that he will destroy the world in one year. Nonetheless, Ministry of Defense government worker Tadaomi Karasuma allows the creature to be the teacher of Kunugigaoka Junior High School's Class 3-E. The students are given weapons specially designed to hurt the creature and are offered a reward of ten billion yen to whoever can assassinate him before graduation. However, none of the students are able to assassinate him due to his Mach 20 speed. Class bully Ryōma Terasaka convinces Nagisa Shiota to wear a grenade filled with pellets. When the creature gets sleepy after assigning the students to write a poem, Terasaka detonates the grenade once Nagisa comes within close range of the creature, but the creature sheds his skin to protect himself and Nagisa from the blast. The creature threatens the other students to refrain from coming up with plans that will harm others. Kaede Kayano names the creature Koro-sensei, seeing him as an "unkillable teacher".