Miyuki Nanase is Hajime Kindaichi's classmate and childhood friend who frequently accompanies him during investigations, often becoming involved in the cases he solves. Their long-standing friendship forms a consistent backdrop to their interactions.

She accompanies Kindaichi to Shanghai after the murder of a Chinese friend's father at a circus, drawing them both into this international case. Later, she reunites with Kindaichi and Inspector Kenmochi at an Opera House anniversary celebration. There, during a rehearsal of "The Phantom of the Opera," new murders attributed to the "Phantom" occur, pulling her directly into another investigation.

Primarily serving as Kindaichi's close companion across settings like school, travel, and formal events, Miyuki is present at critical moments witnessing the start of several murder investigations, maintaining a consistently supportive role.