Gem Starbuck, alias Ai Tachibana in the original Japanese version, serves in the specialized defense unit D-Sentai (renamed Gemini Defense Squad in English adaptations). As an augmented human with cybernetic enhancements, she wields advanced combat capabilities. Her primary role involves piloting specialized Gemini Vehicles (Izen Vehicles) to counter threats. Alongside her brother Jim Starbuck (Zen Tachibana), she leverages their cybernetic link to merge physically and mentally into a composite entity called Gemini (Aizenborg) for precisely 3.5 minutes. This fusion triggers their Gemini Vehicle’s transformation into a heavily armed mechanized form outfitted with offensive weaponry like drills and sawblades, escalating their combat effectiveness against adversaries.

She exhibits a strong protective instinct toward civilians and teammates. During a mission against hypnotized rats, she defied objections to rescue a teammate’s endangered younger sister, sparking internal conflict. Similarly, she contested tactical decisions during a dinosaur attack, arguing against abandoning a rescue. These actions underscore her commitment to preserving lives amid high-stakes battles. Her background as an augmented human centers on repeated confrontations with psychic dinosaurs menacing human civilization.