Seventeen-year-old American David Rutherford joins the Cosmic Culture Club, an international peace initiative. His personality combines recklessness, emotional intensity, and headstrong behavior, making him the group's most hot-blooded member. This temperament fuels his struggle with loss and fear after witnessing the Gradosian attack on Mars that kills his friend Juno. He channels intense hatred and distrust towards Eiji Asuka, holding him responsible for Juno's death and the catastrophe.

David evolves significantly through shared adversity, gradually warming to Eiji and transforming from antagonist to trusted ally. This culminates in him becoming Eiji's wingman, piloting the Gradosian-commandeered SPT-BB-02U Baybull, a general-purpose combat mech armed with knuckle shots and a lasered gun. This serves as his primary vehicle until U.S. military forces seize it on Earth, reflecting persistent Cold War tensions despite the alien threat.

Three years after Earth's Gradosian occupation, David emerges as a prominent guerrilla leader in the resistance during the New York "Ru-Kain 1999" arc. Gradosian commander Ru-Kain uses the repaired Baybull as bait to capture him. David reclaims the mech but abandons it upon discovering a concealed bomb, leading to its destruction. He then transitions to piloting the Earth-built E-SPT-DL-X Doll.

Interpersonally, David harbors unrequited feelings for fellow survivor Simone Reflann. He makes an anguished declaration of love and kiss near the end of the initial arc. Their relationship evolves into a Beta Couple dynamic within the resistance. His interactions with Roanne Demitrich shift from camaraderie to strategic collaboration after Roanne infiltrates the Gradosians as a double agent.

David survives the conflict, witnessing Earth's liberation in the alternative "Kokuin 2000" OVA ending. His journey concludes as part of the collective postwar rebuilding effort.