An tentacled creature suddenly appears and destroys 70% of the Moon, leaving it in the shape of a crescent. The creature claims that within a year, he will destroy the earth too. In class 3-E, the End Class of Kunugigaoka Junior High School, the creature starts working as a homeroom teacher where he teaches his students regular subjects, as well as the ways of assassination. The Japanese government promises a reward of ¥10 billion to whoever among the students succeeds in killing the creature.