Girlfriend of James T. Kirk for about two years during his temporary retirement. Antonia and Kirk met in 2282 while they were both riding horses in Iowa outside Kirk's uncle's barn. They came to live together in a mountain cabin on Earth. In 2284, Kirk decided he would return to Starfleet, and before breaking the news to Antonia, he tried to soften the blow by fixing her breakfast — consisting of toast and Ktarian eggs with dillweed — and serving it to her in bed. As a parting gift, he gave her a horseshoe with a red bow tied to it. The two separated, and Kirk moved to an apartment in San Francisco. He later regretted not asking her to marry him.

Kirk had a chance to relive part of his experience with Antonia during his brief visit to the Nexus temporal anomaly. He decided this time things would be different, and was determined to propose to her. But the experience was not real, and he left the Nexus to meet his destiny.