The "Class Black," 10th Grade of Myōjō Academy is composed of 12 assassins disguised as students and one target: Haru Ichinose. Fully aware of being the prey, Ichinose vows to survive assassination attempts and graduate from the school alive. One of the assassins, Tokaku Azuma, has started building up feelings for Ichinose and switched side to become her protector. Together they have to face the onslaught from their classmates of 11 assassins.