An enigmatic octopus-shaped creature shows up as the homeroom teacher of Class 3-E, the worst class in the Kunugigaoka Middle School. The government assigns the students a secret mission to assassinate the creature, aka “Korosensei”, threatening to destroy Earth next March. The reward is astoundingly 10 billion yen! Will they be able to accomplish their mission? And what is the true goal of Korosensei?