Dr. Tanaka informs Tony that a mysterious epidemic has broken out near the Arc Station. The rampant and deadly disease appears unstoppable, and Tony initiates his own investigation into the cause. Meanwhile, the Self Defense Forces reconnaissance satellites are acting up, and Nagato Sakurai visits Iron Man to ask for his help. Stark and Sakurai join forces, when they discover the Zodiac Mech Aquarius may be behind both.

The plutonium needed to prime the Arc Station is stolen and Tony must don the Iron Man armor and fight against Dio. The two Iron Men must fight to the death, with the fate of Japan hanging in the balance.