Invited to Nazi Germany during the Second World War, Hitler asks Dr. Asagumo to work with him on research into the new "Big X" weapon. Concerned about the potential consequences of Big X's completion, Dr. Asagumo purposely delays the research's development, conspiring with his co-researcher, the devious Dr. Engel. Immediately before the Allies defeat Germany, Dr. Asagumo implants a card engraved on his friend, Shigeru, with the identity of Big X, and is then shot to death by the German army. Twenty years later, the card is found in Shigeru's body and then resides in Tokyo.
Eventually, an entity claiming affiliation with the Nazis emerges, steals the token, and completes the Big X project. Dr. Engel's grandfather has joined the Nazi Affiliation. The completed Big X is then exposed as a drug that can extend the human body without limitation. Recovering Big X from the enemy, Shigeru's son Akira fearlessly confronts the Nazi Alliance and Hans Engel, who are planning to conquer t