The story takes place in an alternate Japan where killing is legal, provided the person possesses an official assassin's license.

The protagonist is Karasuma Dokuhō, an extremely despicable teacher who constantly bullies one of his students, Akabane Kōta. Tired of his teaching profession, Karasuma decides to take the exam to obtain a professional assassin's license.

The problem is that the examiner for the exam ends up being none other than Akabane, the student he used to bully. From then on, the pair embark on a series of confrontations, chases, and absurd situations, mixing frenetic action with dark humor.