"Big X" is a manga series created by Osamu Tezuka, serialized from 1963 to 1966. The story is set in the aftermath of World War II and revolves around the conflict between two factions vying for control of a powerful chemical substance known as "Big X." This substance, developed by the German scientist Dr. Asagumo, has the potential to grant superhuman abilities but also poses a significant threat if misused. The narrative begins with Dr. Asagumo being captured by the Nazi regime, forcing him to develop Big X. After the war, the research falls into the hands of opposing groups, leading to a global struggle for its control.

The protagonist, Aoshima Shigeru, is the son of Dr. Asagumo's assistant. After his father is killed by agents seeking Big X, Shigeru becomes the inheritor of the research. He is transformed into a superhuman by injecting himself with Big X, gaining immense strength, durability, and the ability to grow to a gigantic size. Adopting the identity of "Big X," Shigeru dedicates himself to thwarting the plans of the Nazi remnants and other organizations seeking to exploit the substance for world domination. His primary adversaries include the Neo-Nazi group Schwarze Drachen and their leader, Dr. Engel, who seeks to revive the Third Reich using Big X.

The plot unfolds across multiple arcs, with Shigeru traveling to various locations worldwide to combat the forces of Schwarze Drachen and their allies. Along the way, he encounters a diverse cast of characters, including allies like the journalist Mari and the scientist Dr. Kira, who assist him in his mission. The series blends elements of science fiction, espionage, and action, with a focus on the ethical implications of scientific advancement and the consequences of unchecked power. Themes of redemption, loyalty, and the fight against tyranny are central to the narrative, as Shigeru grapples with the responsibility of wielding Big X while striving to honor his father's legacy. The manga concludes with a climactic battle against Dr. Engel, resolving the central conflict while leaving room for reflection on the broader implications of humanity's pursuit of power.