The first episode of Assassination Classroom , "Assassination Time," introduces a high-stakes premise where Class 3-E students must kill their Mach 20, octopus-like teacher, Koro-sensei, to save the world. The episode focuses on Nagisa Shiota's initial, failed assassination attempt and highlights the unique, nurturing yet lethal dynamic between Koro-sensei and the misunderstood students. For a detailed summary, read the AnimeJindesu review .