Sakuko Kokura (Tomo Sakurai) was a villainess from "The Unsmashable Snowman", the 2-episode premiere of Season 16 of Case Closed (airdates February 26 and March 5, 2007). She was a senior at an art college, with the episode's events having her met Conan Edogawa and company while at a ski resort with her three classmates (Tanji Kiyama, Asaka Onoue, and Kazuya Itabashi) to complete their final project.
Sakuko was shown to display an antagonistic persona to her friends, however, pressuring Kazuya to finish the project quickly due to them leaving in two days and callously inviting all her friends to join her skiing, knowing full well Asaka was unable to ski anymore because of an old injury. Sakuko was later seen being called by someone to meet during a snowstorm, and it was later that Conan and his friends (along with Sakuko's friends) found her drowned to death in a lake left unfrozen by water from a nearby hot spring. While it was initially believed Sakuko's drowning was a result of a snowboarding accident, the truth was uncovered by Conan: Sakuko was killed by Kazuya, with his confession to the deed leading to Sakuko's post-humous reveal as an embittered and jealous villainess.
As Kazuya stated, Sakuko had a long-held crush on Tanji, who himself was already dating Asaka, who was at one point a skilled skiier. Hoping to sabotage Asaka and make Tanji take interest in her instead, Sakuko turned heel by pressuring Asaka into skiing a dangerous slope, knowing full well Asaka was too inexperienced for the slope. As she anticipated, Asaka crashed and broke her leg, with a flashback showing the villainess expressing glee in her plan succeeding. Kazuya learned about his friend's callous deeds after she became drunk one night, expressing bitterness at her actions having failed to drive Asaka away. An enraged Kazuya then decided to kill Sakuko during their final project gathering, luring Sakuko to his room that night and drowning her in the sink after filling it with water from the lake. Kazuya then placed Sakuko and her snowboard inside a large snowball he'd constructed using salt to harden the snow, rolling it into the lake to stage Sakuko's death as a snowboarding accident.