Fujiko Mine is a professional criminal, burglar, and confidence trickster who operates as a freelance agent in the world of international heists. In The Secret of Twilight Gemini, she is depicted as a classic femme fatale, a role that defines her actions throughout the film. Her background is that of a master thief who frequently competes with or reluctantly assists Arsène Lupin III, using her intelligence and physical attributes to pursue valuable treasures. Within this particular story, her primary motivation is the acquisition of the Twilight Gemini jewel, a pursuit that leads her to intersect with Lupin's own quest for the same object.

The film portrays a specific and notable iteration of her personality. Fujiko is highly promiscuous and calculating, leveraging her sexuality as her principal tool. Her tactics are ruthlessly pragmatic; in one of the film's key sequences, she sleeps with Lupin not out of affection, but as a calculated strategy to persuade him to allow her a share of the treasure. This portrayal emphasizes her as a self-serving opportunist who views relationships as transactional. This depiction in The Secret of Twilight Gemini is actually a return to the character's roots, being much closer to her original characterization in the manga, where she is a more openly untrustworthy and sexually manipulative figure, contrasting with some later anime adaptations that present a more classy and witty cat-burglar.

In the story, Fujiko serves as a rival and occasional ally to Lupin, though her alliances are always temporary and subject to her own self-interest. Her actions drive a significant portion of the narrative tension, as her constant potential for betrayal keeps both the characters and the audience uncertain of her true loyalties. While the film introduces a female guest character named Lara, Fujiko's role is distinct; she is not the protagonist's love interest in a traditional sense, but rather a chaotic element who uses her relationship with Lupin to further her own goals. Her key relationships are marked by distrust. Daisuke Jigen is particularly wary of her, viewing her as a harbinger of trouble, and Goemon Ishikawa, despite occasionally working with her, shares a similar distrust. While Lupin is infatuated with her and frequently forgives her betrayals, Fujiko does not reciprocate this devotion, consistently prioritizing the loot over any personal connection.

Regarding her development throughout the film, she does not undergo a significant arc or redemption. Instead, her characterization reinforces her archetypal role as a double-crosser whose loyalties lie only with herself. There is no lasting change to her personality or morals; she remains the same opportunistic thief from beginning to end. Her notable abilities are on full display, including her skills as a master of disguise, a skilled marksman, and an expert in martial arts. She is also highly adept at using her physical charm and emotional manipulation to extract information and cooperation from men. While she can pilot various vehicles and speak multiple languages, her most effective tool in this narrative is her willingness to use her body to achieve her aims, a trait that drew significant commentary when the film was released.