Akiko's backstory also revealed that she was the former teacher of Minako Mochizuki, who died three years prior in what was officially ruled a suicide by hanging. Akiko, however, believed that Minako had actually been murdered by two of her fellow teachers, one of whom was music teacher Sugiyama, as Minako had approached her before her death with information that Sugiyama and another teacher (who she refused to name) were illegally using their influences to get students into schools.
Enraged at the belief that Sugiyama had murdered Minako, Akiko anonymously set up a ski lodge trip to kill him and his accomplice in revenge. Along with Sugiyama, Akiko invited three other school employees and friends (Kohei Shimoda, Ryuichi Sakai, and Minori Nakamura) as well as journalist Atsushi Mori, who held a vendetta against the school for (in his mind) failing to help Minako. Ran and Sonoko, along with Conan Edogawa, also joined the group after running into Akiko and her friends while skiing. Unbeknownst to the group at the time, Akiko had previously lured Sugiyama to the lodge and strangled him to death, later hiding his body outside the lodge.
After arriving at the lodge, Akiko used Sugiyama's corpse to stage her own attack as she and Sonoko were fixing the beds, disguising the body to look like her. When Sonoko came in and saw the body, Akiko snuck up behind her former student, drugging her with chloroform before strangling her with a rope. Afterwards, Akiko used a trick she set up with kite string and a rubber band to set up Sugiyama at the front door, with the band eventually breaking in the freezing cold and the doorbell being rung by Sugiyama's body, leading to the discovery of his corpse by the rest of the group.
Later on, after Kohei panicked and locked himself in his room, Akiko convinced him to let her into his room, phoning him and claiming she would tell him who the killer was if he left her in. Once inside, Akiko used the wig she was wearing to strangle Kohei, having tied part of the wig hair into a braid. She then left the room, setting up Kohei's phone to ring so his body would be discovered right away and it would appear that his murderer hide the weapon used to kill him, clearing her of suspicion.
But Conan Edogawa was able to deduce Akiko's guilt and used his voice modulator and portable earring phone to have Ran reveal her former teacher as the killer, much to her shock and heartache. After revealing how Akiko had committed her crimes, as well as how her wig would contain traces of Kohei's blood, Akiko took off her wig and confessed, stating that while what she'd done was wrong, she'd done it all to avenge Minako and had arranged the trip to find out who Sugiyama's cohort was, who she realized was Kohei. Akiko then ranted that she couldn't forgive Sugiyama and Kohei for betraying and killing a student who admired them so dearly, while also showing remorse for attacking Sonoko to further her scheme. The police were eventually able to arrive at the lodge and presumably arrested Akiko offscreen.
- In the English dub, Akiko's name is translated to Anne Preston and is voiced by Jamie Marchi.
- Jamie Marchi (Akiko's English dub actress) also appeared in Case Closed's first season as the villainous Businesswoman and voiced Case Closed villainesses Reika Yotsui, Kazumi Tatsumi, Kyoko Saegusa, Keiko Yabuuchi, and Mizue Ichikawa.