Riddle Story of Devil

Tokaku Azuma transfers to Myoujou Academy, an elite private girls' boarding school, where she's part of Class Black, a group of 12 students assigned to kill Haru Ichinose, their classmate. The person who successfully kills Haru will be granted their deepest desire, but each assassin has only one chance and will be expelled if they fail. Tokaku's initial intention is to kill Haru, but she starts to develop feelings for her target, which puts her at odds with the rest of Class Black.