Yoko Okino attended Kohnan High School and dated Akiyoshi Fujie. Her manager, Eiichi Yamagishi, persuaded Akiyoshi to break up to support her aspiring idol career, though Akiyoshi never stopped loving her and planned to reunite.

She debuted in the pop idol quartet "Earth Ladies" with Kaoru Kusano, Yuki Takeno, and Terumi Hoshino. After the group found success and disbanded for solo pursuits, Yoko maintained her popularity as a solo idol and actress, staying close to her former bandmates.

Yoko first sought Kogoro Mouri's help when a stalker entered her apartment, leading to a case where Kogoro, Ran Mouri, and Conan Edogawa discovered Akiyoshi Fujie's body, staged to look like murder. Conan deduced Akiyoshi committed suicide by impaling himself on a knife, despairing after mistaking idol Yuko Ikuzawa for Yoko. Conan's resolution protected Yoko's career.

Following this, Yoko continued her successful entertainment career in film and television. She became a recurring acquaintance of Kogoro, Ran, and Conan, frequently inviting them to events, dinners, or parties. She also facilitated Kogoro's appearances on her television shows and commercials.

Despite her fame, Yoko remains modest and friendly, known for her loyalty to friends and fans, contributing to her enduring appeal. Ran addresses her as "Yoko-chan" or "Yoko-san," while Yoko calls Ran "Ran-san." Kogoro, a devoted fan, affectionately calls her "Yoko-chan," and she formally addresses him as "Mouri-san."