Stephen Sandor, also known as Shiro Sanada, commands the roles of Chief Science Officer and First Mate on the Space Battleship Yamato. A top MIT graduate, he advanced through the National Space Defense Academy and volunteered for the United Nations Cosmo Navy. Assigned to the 9th Strategic Division, his exceptional analytical skills and logical thinking made him central to the Yamato Plan.

As First Mate, he acts as Captain Juzo Okita's primary advisor, overseeing scientific analysis, information assessment, engineering, and technical operations. His rigorous logic provides vital situational assessments during missions. He maintains a reserved, professional demeanor, often acting as a stabilizing influence on more emotional crew members like Susumu Kodai.

After Earth's restoration following the Gamilas conflict, Sandor detects a mysterious transmission warning of the approaching White Comet Empire. Analyzing data with Kodai and Daisuke Shima, he identifies the imminent threat and urgently advocates for preemptive action to the Earth Defense Council. When the council dismisses the threat and orders Yamato's decommissioning, he supports the crew's decision to mutiny and reclaim the ship. His technical expertise is crucial for Yamato's unauthorized launch.

During the mission against the Comet Empire, Sandor assumes greater command responsibilities as casualties rise. At the climax, he leads an infiltration team into the enemy's core fortress, Gatlantis. Recognizing that manual detonation is required to destroy its energy core, he sacrifices himself alongside Hajime Saito to ensure the core's destruction, disabling Gatlantis' primary systems.