Black Jack boards an undersea train pursuing Detective Shunsaku Ban to collect an unpaid fee for treating the detective's gunshot wound, reflecting his established practice of demanding high payments. During the journey, his exceptional surgical skill emerges as he performs emergency brain surgery on the critically injured scientist Dr. Narzenkopf after a confrontation with weapon smugglers, showcasing his capability to handle complex procedures under dire circumstances.

He actively participates with the passengers in their struggle to survive the escalating crises aboard the train and their subsequent displacement to the ancient civilization of Mu. Following the defeat of the sorcerer Sharaku in the past, he chooses to remain temporarily in the Mu era to provide medical care to the injured, indicating a sense of responsibility despite his usual mercenary demeanor.

His appearance includes distinctive black-and-white hair and visible scars across his body, most notably his face. These are the result of childhood trauma from a landmine explosion that killed his mother and nearly destroyed his body. Dr. Jotaro Honma treated these injuries, inspiring his path to becoming a surgeon. Black Jack operates without a medical license, having lost it due to insubordination when he saved a patient against orders. While he typically charges exorbitant fees, he possesses a complex moral code and will perform surgeries for free if deeply moved by a patient's suffering. He is highly perceptive, capable of rapid diagnosis, and utilizes his surgical tools with precision, sometimes employing them defensively. He shares his home with Pinoko, an adopted daughter he created from a teratomatous cystoma.