The acting troupe was visited by Kogoro and Ran Mouri, Sonoko Suzuki, and Conan Edogawa, as two of the actors in the troupe were Tamanosuke Ito and Renge Kataoka (old friends of Conan and company). Their visit led to the gang learning of frightening pranks being committed by someone they believed to be a phantom, bearing witness to Romi nearly being crushed under a set piece. The set piece was of a chandelier set to collapse in the play's beginning, leading Conan to realize the were mirroring the events of Phantom of the Opera.
Despite worries from Tamanosuke, Romi remained adamant on performing as the play's heroine, only to end having to be replaced by Renege (who the prankster wanted to perform in Romi's place) after Romi found herself unable to speak during the opening night performance; a result of having the water she used to clear her throat tampered with by the "phantom", who also appeared during the performance. The following day, stage setting chief Katsuo Naboshima was found stabbed to death in a park, with Tamanosuke being arrested for the murder after he was found unconscious next to his body, holding a bloody knife and wearing a phantom mask covered in blood. It was later believed that the play's sponsor, Tatsuhiko Rausu, had killed Katsuo and framed Tamanosuke out of a desire to earn Renge's affections (both men having a crush on Renge), with Romi claiming she had lied about being seen by Tatsuhiko at the park while practicing her singing on the night of the murder further implicating him.
RevealEditHowever, Conan's investigation into the murder ultimately revealed the truth: Romi was Katsuo's true killer, and was additionally behind the various pranks during the play. Her motivation was revealed to be revenge against Tatsuhiko, as his father (the former head of Rausu Companies) was responsible for her father losing his business. Romi's father died shortly afterwards followed by her mother, with Romi blaming Tatsuhiko's father for her loss.
Romi eventually began formulating her plan for revenge after joining the troupe Katsuo was funding, initially planning to simply sabotage the play to destroy Tatsuhiko's reputation. Romi intended for her schemes to result in Renge taking over her role and failing in it, only for that to backfire when Renge's performance was met with praise. Soon after, Romi was caught by Katsuo holding the projector she used to make the "phantom" appear during the performance, intending to use his knowledge to blackmail her. Wanting to both take her revenge and keep Katsuo silent about her actions, the evil Romi lured Katsuo to the park with a note, waiting until he was standing by the shrine she instructed him in the letter to meet her at before stabbing her in the back of the neck with a knife. Romi then waited until Tamanosuke arrived (having left him a note as well) and knocked him out with a rock, setting the scene to look like he had been attacked and set up by Tatsuhiko, using a strip of performance tape from the theatre with Tatsuhiko's fingerprints to further her scheme.
Romi additionally planted the equipment she used for her theatre pranks in the trunk of Tatsuhiko's car and deceived the police into believing he didn't have an alibi for the murder, with the latter detail leading Tatsuhiko to realize she was the culprit. After escaping police custody and finding evidence at the theatre that Romi was at a nearby water cavern, Tatsuhiko went to the scene and was promptly knocked out and tied up by Romi, who had lured Tatsuhiko to the location as part of her plan to kill him. With Tatsuhiko unconscious, Romi returned to the theatre, where the villainess (in her phantom disguise) knocked Renge out with chloroform before taking her to the cavern as well, where she was ultimately cornered by Conan, Tamanosuke, Ran, and Sonoko.
After Conan knocked out and impersonated Sonoko to reveal Romi as the culprit, Romi unmasked herself and confessed to her crimes, revealing her scheme as a vengeful plot against Tatsuhiko and how she hadn't intended for her plot to involve murder in the initial phases. Romi also revealed how Katsuo's blackmail attempt spurned her murderous plot, as well as how she'd planned to kill Renge and Tatsuhiko and stage their deaths as a double suicide to escape police capture. Instead, however, Romi dropped the still unconscious Renge and her knife before jumping into the water in an attempt to drown herself. After being rescued by Conan and Tamanosuke, Conan (while impersonating Sonoko) chided her actions as being unjustified despite the death of her parents, as well as how he believed she left clues to her whereabouts partially in an attempt to be stopped. Romi subsequently broke down in tears, and was later shown being arrested.
- Junko Minagawa also voiced the evil Yoshie Taira, who appeared in Season 11 of Case Closed.