At the elite boarding school Myoujou Academy, there is a special "Class Black." Disguised as a regular class, it serves a single purpose: assassination. At the center of Class Black, one student is the target while the others are assassins who are all eager to make the kill. The student who successfully assassinates the target will have any wish granted, but they only have one chance to do so; expulsion awaits those who miss their mark. Azuma Tokaku, an apathetic assassin-in-training, finds herself transferred to the latest Class Black with 12 other girls. One girl stands out from the rest—Haru Ichinose, a cheerful girl who is idealistically insistent on making friends and graduating. As expected, the students discover that Haru is indeed the target and begin to plan their assassination. However, Azuma feels a growing fondness for Haru and is drawn to a different course of action. Now, for the first time in her life, she has found a cause to fight for.