David Rutherford is a 17-year-old American member of the Cosmic Culture Club, an international student exchange program visiting a United Nations base on Mars in 1996. He emerges as one of the few survivors of the Gradosian attack that destroys the base and kills most participants, including his close friend Juno. Juno's death ignites fierce hatred and distrust toward Eiji Asuka, whom David blames for the tragedy.

Reckless, emotional, and headstrong, David initially clashes with Eiji, prioritizing the immediate survival of the remaining club members over Eiji's pacifist ideals. This conflict drives his confrontational attitude. Shared hardships endured during the perilous journey from Mars to Earth gradually forge mutual respect, transforming David into Eiji's trusted wingman. He commands the Gradosian SPT-BB-02U Baybull, a general-purpose combat mecha stolen by Eiji.

During their ordeal, David develops romantic feelings for fellow survivor Simone Reflann. These feelings culminate in an anguished declaration of love and a desperate kiss near the end of the initial conflict period, establishing them as a secondary couple within the group.

Following Earth's invasion and occupation by the Gradosian Empire, a three-year timeskip finds David leading guerrilla resistance operations in New York City during 1999, his fighting spirit undimmed despite Earth's subjugation. Gradosian commander Ru Kain deploys the repaired Baybull as bait in a tactical ploy. David reclaims his former mecha but is forced to abandon it upon springing an implanted explosive trap. The Baybull's destruction necessitates his transition to the Earth-developed E-SPT-DL-X Doll as his new combat unit.

His character arc concludes with active participation in Earth's liberation campaign. He survives the conflict and achieves a positive resolution to his relationship with Simone, solidifying their bond by the series' conclusion in the alternative ending presented in the OVA.