Okino Youko is a young pop star idol who is a regular focus of worship by Mouri Kogorou. She has a number of cameos throughout the series, mostly as a prominent guest at some social gatherings which turn into criminal cases.

Youko started her idol career as a member of the quartet "Earth Ladies", along with Kusano Kaoru, Takeno Yuki, and Hoshino Terumi. The team was quite successful, but after some time they disbanded to pursue their own careers. Youko has remained successful and quite popular in the pop idol and acting business.

Youko first met Conan, Mouri and Ran when she asked for Mouri's help in apprehending a stalker who had even penetrated her apartment (and of course, Mouri would not hesitate to take the case). But in the apartment they found an unknown man impaled upon a knife, turning this case into a murder investigation. Soon, however, Conan figured out that the 'victim' had actually committed suicide: The man was Fujie Akiyoshi, Youko's old boyfriend who still loved her. Due to a fatal misunderstanding, however, Fujie fell into despair and plunged himself on to the knife, making it appear as if he had been murdered in order to take revenge on Youko. Luckily, Conan found out the truth before damage could be inflicted on Yoko's career.

Overcoming her grief, Youko has carried on her career and has remained a friend and valuable contact to Conan and Mouri in the TV and idol industry ever since.