During World War II, Dr. Asagumo is summoned to Nazi Germany, where Hitler tasks him with developing the ultimate weapon, Big X. Worried about the catastrophic consequences of its completion, Asagumo deliberately slows the research alongside his sinister colleague, Dr. Engel. On the eve of Germany’s defeat, Asagumo embeds a card containing Big X’s secrets into his son, Shigeru, before being executed by German forces. Two decades later, the card is found within Shigeru, who is now residing in Tokyo. A faction aligned with the Nazis soon steals the card and finalizes the Big X project, with Dr. Engel’s grandson involved in the alliance. The completed Big X is revealed to be a substance that allows unlimited human physical expansion. Shigeru’s son, Akira, boldly confronts the Nazi Alliance and Hans Engel to reclaim Big X and thwart their global conquest plan.
