Yukiko Mori (Case Closed)

Yukiko Mori (Akiko Yajima) is the villainess of "The Silent Loop Line", episode 6.24 of Case Closed (airdate August 23, 1999). She was a new employee at an advertisement design company and was close with three fellow co-workers: Seiji Kurata, Shizuka Kawai, and Kiyomi Hashimoto.
Prior to the episode's events, the four reconvened at the office to fix an advertisement that Yukiko had made a mistake with. Kiyomi left early and Yukiko went with Seiji and Shizuka to take the subway home. But while on the train, the three discovered Kiyomi's body, her having been poisoned to death. Kogoro Mouri (who was on the train with his daughter Ran and Conan Edogawa) investigated the murder along with inspector Juzo Megure and detective Wataru Takagi. The case was further complicated by the fact that all three of Kiyomi's co-workers had a motive to kill her.
But ultimately, Conan deduced that Yukiko was the true murderer. Yukiko was angry with Kiyomi for stealing her boyfriend from her and devised a plot to kill her, beginning with intentionally making a mistake at work so Kiyomi and the others would have to work on that day. Yukiko then damaged Kiyomi's CD player so she would be able to loan her her own, having placed a needle coated in blow-dart poison inside the headphones. Kiyomi became injected with the poison while on the train and died, and when Yukiko arrived at the train station with her co-workers, Yukiko went to get a juice from a vending machine, allowing her to get on the train after her friends and retrieve the poisoned headphones before Kiyomi's body was discovered.
The headphones became stuck due to Kiyomi's body leaning against the wall, causing Yukiko to break the headphones and wrinkle Kiyomi's shirt collar. To cover her tracks, Yukiko fixed Kiyomi's shirt collar and feigned shock so she would be left alone, allowing her to remove the poisoned needle from the headphones and hide it in her soda can holder. When Conan impersonated Kogoro to reveal the truth, Yukiko denied everything due to having gotten rid of her murder weapon, but Conan revealed the remaining piece of evidence that proved Yukiko's guilt: the disc inside the CD player that had that day's date on it, contradicting Yukiko's claims that she had never loaned Kiyomi anything. 
Defeated, Yukiko collapsed to the floor and confessed to killing Kiyomi, revealing her anger at her for stealing her boyfriend from her and that she'd chosen that day to commit her villainous plot since it was his birthday. Yukiko was later arrested, and it was revealed by Takagi that Kiyomi had obtained the blow-dart poison while on a trip to South America.
Category:1990s
Category:Anime Villainess
Category:Brunette
Category:Hero's Friend
Category:Makeshift Weapon
Category:Murderer
Category:Murder: Poison
Category:Villainous Reveal
Category:Fate: Arrested