When the moon is irreversibly transformed into a crescent shape by a mysterious yellow tentacled being, the world is thrown into chaos. This creature, capable of incredible speed, declares its intention to also destroy Earth within a year unless a strange demand is met: to teach at Kunugigaoka Junior High School. Tasked with the impossible mission of assassinating their new teacher, nicknamed Koro-sensei, the students of Class 3-E face not only the pressure of saving the world but also the daily struggles of discrimination and low expectations. As they are tutored in both lethal skills and academics by their target, the students learn to challenge their own limitations and aim for a victory no one thought possible.