Kyōko Tachibana is a freelance lawyer who appears in the twenty-second entry of the Case Closed film series. She is twenty-nine years old and works without a fixed office, taking on cases through her mobile phone, a style sometimes referred to as a mobile lawyer. She has slightly wavy short hair, sharp eyes, and round glasses. Her background is rooted in the judicial system; she once ran a law firm where she employed a judicial intern named Fumikazu Haba, with whom she developed romantic feelings. Haba was later arrested during the NAZU hacking case and was believed to have committed suicide while in custody, though in truth the Public Security Bureau had faked his death to protect him. Believing Haba had died because of the police, Tachibana harbored a deep resentment toward law enforcement.

In the story, she is introduced when Ran Mouri and her mother Eri Kisaki are desperately searching for a lawyer willing to defend Kogoro Mouri, who has been arrested as the prime suspect in a bombing at the Edge of Ocean conference center. Tachibana volunteers to take the case despite her poor track record in public security cases, having lost every previous one. Her role is initially that of a helpful if seemingly ineffective attorney, but her true motivation is more complicated. She is secretly cooperating with the police while at the same time intending to sabotage the defense in order to exact revenge on the authorities she blames for Haba's apparent death. Throughout the film, she maintains a calm, professional demeanor, but her actions are driven by a personal vendetta.

Her key relationships include the Mouri family, especially Eri Kisaki and Ran, as well as Conan Edogawa, who observes her behavior with suspicion. She is also connected to the prosecutor Makoto Kusakabe, who was Haba's former collaborator, and to the Public Security Bureau officer Toru Amuro, though she interacts with him only indirectly. Her relationship with Haba is the emotional core of her character arc. When it is eventually revealed that Haba is still alive, her motivation shifts, and she begins to let go of her grudge.

In terms of development, Tachibana evolves from a character who appears to be a somewhat unreliable lawyer into a more complex figure whose actions are shaped by grief and a sense of injustice. By the end of the film, she comes to terms with the truth and her role in the broader events. Her notable ability is her legal expertise, particularly in handling cases involving public security, though the film emphasizes that her prior losses were not due to incompetence but rather the circumstances of those cases. She also demonstrates keen observation and the capacity to operate within a system she distrusts.