"Riddle Story of Devil" is a 12-episode anime series set in a prestigious all-girls boarding school, Myoujou Academy. The narrative centers on Tokaku Azuma, a skilled assassin who transfers to Class Black, a group of 12 students, each with a hidden agenda. The class is part of a secret assassination program where the students are tasked with eliminating their classmate, Haru Ichinose. The last assassin standing will be granted any wish they desire. Tokaku, however, defies expectations by choosing to protect Haru instead of participating in the deadly game.

Haru Ichinose is portrayed as a cheerful and kind-hearted girl, seemingly unaware of the danger surrounding her. Her innocence and optimism stand in stark contrast to the ruthless nature of her classmates. As the series progresses, it becomes clear that Haru’s life is tied to a deeper mystery, and her survival becomes a focal point of the story. Each episode introduces a new assassin with unique skills and motivations, leading to intense confrontations and strategic battles.

The assassins in Class Black are diverse in both personality and methods, ranging from physical combatants to manipulative schemers. Notable characters include Nio Hashiri, the class representative who orchestrates the assassination game, and Shiena Kenmochi, a sniper with a tragic past. The interactions between the assassins and their attempts to outwit one another drive the tension and suspense of the series.

As Tokaku continues to protect Haru, her own backstory is revealed, shedding light on her reasons for defying the program. The series explores themes of trust, loyalty, and the moral ambiguity of survival. The dynamic between Tokaku and Haru evolves from one of reluctant protection to genuine camaraderie, adding emotional depth to the otherwise action-driven plot.

The narrative builds toward a climactic confrontation, with the true nature of the assassination program and Haru’s significance gradually unveiled. The series concludes with a resolution that ties together the fates of the main characters while leaving room for interpretation regarding the broader implications of the events at Myoujou Academy.