Rock Nasenkopf is the adopted son of the prominent mechanical engineer Dr. Narzenkopf, designer of the Marine Express undersea train. As the elder son, Rock pilots this vessel on its inaugural trans-Pacific test run from Los Angeles to Japan, relying on technical expertise to manage systems and counter emergencies like undersea volcanic eruptions threatening the tunnel. He displays unwavering loyalty to his father, especially after Dr. Narzenkopf suffers a critical head injury during a confrontation with financier Director Credit. Though emotionally distraught, Rock focuses on securing medical aid for his father while simultaneously helping other passengers thwart a hijacking plot by the smuggler Skunk, prioritizing passenger safety.

Mid-voyage, Rock experiences a vision of a woman revealed as Empress Sapphire of ancient Mu. This foreshadows the train's displacement 30,000 years into the past upon reaching a rest-stop island. In this era, Mu suffers under the tyrannical sorcerer Sharaku, who overthrew Sapphire. Rock allies with the deposed Empress and her supernatural guardian, the flying white lion Leo, organizing resistance against Sharaku. Donning ancient warrior armor, he shifts from technician to military leader, spearheading combat alongside survivors from the train.

Following Sharaku's defeat, Rock chooses to remain permanently in the past. He marries Empress Sapphire, becoming her consort, and pledges to rebuild the Mu Empire. This decision severs his ties to the present, abandoning his former life and responsibilities. Only detective Shunsaku Ban returns to the contemporary era, leaving Rock's fate as part of Mu's restored legacy.