Mr. Kuroshio is a prominent businessman owning significant local enterprises, including the shipyards employing Hayato Arashiyama's father. During a thunderstorm, he and his wife become trapped in a car accident, leading to their rescue by Hayato and his father. The group shelters in an abandoned mansion, encountering a skeletal figure claiming to be the captain of a phantom ship. This captain seeks vengeance for a decade-old tragedy involving the murder of his crew, his own poisoning, and the deliberate burning of his ship with his wife and child aboard, implying Kuroshio's involvement.

After a giant robot called the Golem destroys part of the city and kills Hayato's parents, Kuroshio positions himself as the leader of the volunteer defense force against the phantom ship threat. He rises to become the city's most influential figure, organizing its defense. Hayato joins this force seeking revenge but accidentally discovers an underground passageway in Kuroshio's residence. This reveals a disconnect between Kuroshio's public actions and hidden motives, indicating he is not an ally. Hayato's life is endangered as he uncovers Kuroshio's true role in the conspiracy.

Kuroshio is ultimately revealed as the orchestrator of the phantom ship attacks and the city's destruction, positioning him as the primary antagonist. His background as a powerful industrialist provides access to advanced technology and military resources, like the tanks deployed during the crisis. His character arc centers on maintaining a facade of protective leadership while secretly driving the conflict for personal or strategic gain.