Yoko Asanuma (Youko Asagami) is the villainess of "Snow Woman's Legend Murder Case", episode 4.12 of Case Closed (airdate March 9, 1998). She was an aspiring actress and the stunt woman for Akiko Kinoshita, who was famous for portraying the "Snow Woman" in a popular film series.
While she initially appeared close with Akiko, Yoko secretly held jealousy and resentment towards Akiko, as she was originally in the running for the role of the Snow Woman. Feeling she would always be outshined by Akiko, Yoko plotted to kill Akiko during a vacation to the mountains, with the women staying at a lodge Yoko previously worked at.
While out skiing with Akiko, the evil Yoko drugged Akiko's drink with sleeping pills, dressing her in the white kimono gown her film character wore before burying her in the snow to freeze to death. After returning to the lodge in her skiing gear (which included a full-face mask), Yoko climbed out her room window and re-entered the house dressed in Akiko's skiing outfit, posing as her and faking that she was ill and had to go to bed early, later using an automated moving serving tray the lodge while having drinks with Kogoro Mouri to further her ruse.
Later that night, Yoko forged a suicide note to make it appear that Akiko killed herself out of fear that she had contracted lung cancer like her father, with the snow's sudden stopping resulting in Akiko's body being found. Her death was initially ruled as suicide, but Conan Edogawa noticed how roughly Yoko had prepared Akiko's body (namely how she tucked her hair into her kimono) and impersonated Kogoro in order to reveal the truth. Yoko ultimately admitted to killing Akiko, revealing her resentment for living in her friend's shadow and tearfully bemoaning how her acting career was now ruined. Yoko was presumably arrested offscreen.