Carla is a resident of the World of Darkness who appears as a central guest character, known for her volatile and passionate nature, which drives much of the conflict in the story. Her background is rooted in a deep, unrequited love for Rupa, a fellow resident of the World of Darkness and her childhood friend. Carla's feelings for Rupa began when they were young, and they were once close companions. However, their relationship soured dramatically when Rupa informed her of his arranged engagement to Lum, an oni girl from another world whom he had never met. Upon hearing this news, Carla became consumed by jealousy, transforming from a childhood friend into a relentless and aggressive pursuer. This event marked the beginning of a decade-long campaign to win Rupa's heart, characterized by a disturbing pattern of desperate romantic gestures followed by violent attacks when her advances were rejected. Her behavior, while born from genuine affection, became self-sabotaging, as her own aggressive actions were the primary reason Rupa grew to fear her and distance himself.

In terms of personality, Carla is defined by an all-consuming passion and an almost frightening lack of restraint. She throws herself completely into her obsession with Rupa, driven by a single-minded determination that borders on fanaticism. She is headstrong, temperamental, and prone to explosive rages during which she will wildly attack the source of her anger with any weapon at her disposal, and she is almost always seen carrying heavy armaments. Despite her jealousy and violent tendencies, there is a certain straightforwardness to her; she is utterly transparent in her desires, showing frustration when others, like Ataru, overcomplicate their own romantic problems. Carla has significant flaws, including a stubborn refusal to admit when she is at fault and a deep reluctance to apologize. Even when Rupa bluntly states that he dislikes her because she constantly attacks him, she cannot acknowledge that her behavior is wrong. This combination of traits makes her her own worst enemy, as her inability to control her temper or accept blame continuously pushes Rupa further away.

Carla's primary motivation throughout The Final Chapter is to stop Rupa's wedding to Lum and claim him for herself. This goal leads her directly into the story when she thwarts the wedding ceremony. Initially, she takes Ataru hostage, using him to pose as a fake engaged couple to gain entry to the wedding hall. When this plan fails, she resorts to brute force, blasting her way into the ceremony with a powerful firearm. Her role in the story is that of a chaotic and disruptive force. By attacking the wedding, she inadvertently creates a major misunderstanding between Ataru and Lum, leading to a catastrophic fight where they break off their relationship. This event is the catalyst for the film's central conflict: an ultimatum from Lum that forces Ataru into a high-stakes rematch of their first game of tag. After the failed wedding, Carla, feeling rejected and with no reason to stay in her homeworld, returns to Earth with Ataru and the others. Once on Earth, her role shifts; she inadvertently becomes an unwitting instigator when she offers mushrooms from the World of Darkness for a hotpot, neglecting to mention that they grow explosively when exposed to heat and light. This leads to a giant mushroom forest overrunning Tomobiki, creating the dangerous stakes for Lum's final game of tag with Ataru.

The most significant relationship in Carla's life is with Rupa. Their dynamic is a dark mirror of the central romance between Ataru and Lum, characterized by a male lead who runs away from a persistent, electrically-powered woman. However, Carla amplifies Lum's traits to an extreme, making her far more aggressive, possessive, and violent. Rupa, for his part, is terrified of Carla's murderous jealousy, which has been his reality for ten years. He admits that he does have feelings for her but hates her violent nature. It is only through the events of the film that they find a resolution. After days of the tag game, Rupa confronts Carla and, instead of simply removing the mushrooms, declares that he will only do so if she agrees to return to the World of Darkness with him as his bride. He finally confesses his love for her, and once Carla comprehends this, she immediately forgets all her grievances and embraces him, her decade of desperate pursuit ending in joyful reconciliation. She also has a significant, though temporary, alliance with Ataru, working with him to crash the wedding. She observes his stubborn refusal to admit his love for Lum and finds it somewhat baffling, given how much simpler it would be for him to just say the words. Her relationships with other characters, such as Lum and Ran, are largely adversarial or incidental, as she is focused entirely on her own goal.

Carla demonstrates several notable abilities. As a resident of the World of Darkness, she is presumably adapted to that environment, but her most prominent skill is her expertise with heavy weapons. She carries a large bazooka-like firearm and uses it with reckless abandon, creating explosions and destruction to achieve her goals. Her knowledge of her homeworld's ecology includes an understanding of its dangerous mushrooms, though she carelessly fails to warn others of their properties. Her personal development throughout the film is significant, as she transforms from a violently jealous antagonist to a woman whose long-suffering love is finally requited. The resolution of her character arc occurs when she and Rupa confess their true feelings for each other. In the end, having finally heard the words she waited a decade for, Carla flies away from Earth on the back of one of Rupa's flying boars, leaving with him to return to the World of Darkness.