Akuma no Riddle: Riddle Story of Devil

At Myojo Private School, an elite all-girls boarding academy, the Class Black is comprised of thirteen students, twelve of whom are assassins. Their prey is the thirteenth student, Haru Ichinose, an upbeat girl who vows to survive school and graduate unharmed! Enter Tokaku Azuma, a cold-blooded killer who transfers from another school to kill Haru.