"Akuma no Riddle: Riddle Story of Devil" is a manga series set in a prestigious all-girls boarding school, Myoujou Academy, which harbors a secret class known as the "10th Year Black Class." This class is composed of twelve students, eleven of whom are assassins tasked with eliminating the twelfth student, Haru Ichinose. The assassins are promised any wish they desire if they succeed in killing Haru, but they must do so without being caught by the school's strict rules. Each assassin possesses unique skills and backgrounds, making them formidable opponents.

Haru Ichinose, the target, is a cheerful and seemingly ordinary girl who remains unaware of the danger surrounding her. Her classmate, Tokaku Azuma, is one of the assassins but quickly develops a protective bond with Haru, choosing to defend her against the other assassins. Tokaku's decision to protect Haru complicates the dynamics of the class, as the other assassins begin to devise increasingly elaborate plans to eliminate their target while avoiding detection.

The narrative unfolds through a series of assassination attempts, each orchestrated by a different assassin. These attempts are interspersed with flashbacks that reveal the motivations and backstories of the characters, adding depth to their actions. Themes of trust, loyalty, and morality are explored as the assassins grapple with their missions and personal desires. The tension escalates as alliances shift, and the true nature of Haru's past is gradually unveiled, raising questions about her role in the deadly game.

The story maintains a balance between action and psychological drama, with each chapter focusing on the interactions between Haru, Tokaku, and the other assassins. The setting of the isolated academy amplifies the sense of claustrophobia and urgency, as the characters are constantly under surveillance and must navigate the school's strict regulations. The series concludes with a resolution that ties together the fates of the main characters, providing closure to the high-stakes conflict while leaving room for reflection on the choices made throughout the story.