A mysterious octopus-like creature appears one day and destroys 70% of the Moon, threatening to annihilate Earth within a year. Strangely, he takes a job as the homeroom teacher of Class 3-E at Kunugigaoka Junior High School. Dubbed "Koro-sensei," this seemingly invincible being teaches the so-called misfit students while giving them one mission: assassinate him before graduation to save the world—and earn a massive reward.

Despite the assassination attempts, Koro-sensei proves to be a phenomenal teacher, helping his students grow academically, emotionally, and socially. As the school year progresses, the students begin to uncover the truth behind Koro-sensei’s origins and his true motives. What begins as a deadly game becomes a moving and suspenseful tale about growth, redemption, and the deep bond between teacher and students.