"Black Jack 21" is a continuation of the "Black Jack" series, based on the manga by Osamu Tezuka. The story centers on Black Jack, an unlicensed but highly skilled surgeon who operates outside the conventional medical system, charging exorbitant fees for his services. Despite his morally ambiguous methods, Black Jack is driven by a deep sense of justice and a desire to save lives, often taking on cases that others deem impossible.

The narrative unfolds as Black Jack is drawn into a web of intrigue involving a secret organization known as "Noir," which seeks to manipulate global events through advanced medical technology and unethical experiments. The series explores Black Jack's past, revealing his connection to a tragic incident during his medical training that left him scarred physically and emotionally. This incident ties directly to Noir, as the organization's leader, Dr. Kiriko, was involved in the event that shaped Black Jack's life.

Throughout the series, Black Jack is accompanied by Pinoko, his young assistant and adoptive daughter, who provides emotional support and comic relief. Together, they confront a series of complex medical and ethical dilemmas, often involving Noir's machinations. The story delves into themes of morality, the limits of medical science, and the consequences of unchecked ambition. Black Jack's encounters with Noir force him to confront his own principles and the darker aspects of his past, culminating in a climactic showdown that tests his skills and resolve.

The series maintains a balance between episodic medical cases and an overarching narrative, blending suspense, drama, and action. Black Jack's character is portrayed as enigmatic and multifaceted, with his motivations and actions often challenging conventional notions of right and wrong. The supporting cast, including recurring characters like Dr. Honma and Kiriko, adds depth to the story, highlighting the moral ambiguities and personal stakes involved in Black Jack's world. "Black Jack 21" serves as both a standalone narrative and a deeper exploration of its protagonist's origins, offering a compelling mix of medical drama and conspiracy thriller.