Masayo Yaguchi is the manager of the renowned stage actress Juri Maki in the film Detective Conan: Magician of the Silver Sky. She is a woman in her early thirties who wears glasses and has a quiet, somewhat unassertive demeanor. Her personality is described as inattentive and inefficient, which frequently draws harsh criticism from her employer. Juri often scolds her publicly, causing Masayo to feel humiliated and marginalized. Unlike Juri’s skilled and confident makeup artist Natsuki Sakai, Masayo lacks the same level of competence and is often overshadowed in her duties.

Her primary motivation is simply to fulfill her role as a manager, though she appears to endure her position with a resigned, luckless attitude. She does not express any active resentment toward Juri despite the constant belittlement, and she shows no particular ambition or desire for change.

In the story, Masayo becomes an early suspect when Juri is poisoned after eating a chocolate that had been prepared for her. The chocolate is traced back to Masayo, who had brought it, making her the prime suspect in the investigation. However, she is defended by Natsuki, who points out that many people present had reason to want Juri dead. Ultimately, the real culprit is revealed to be Natsuki, and Masayo is cleared of suspicion.

Her key relationships are limited to her professional ties. She works closely with Juri, but the dynamic is one-sided and abusive. She also interacts with Natsuki, who is more capable and seems to pity her. Masayo does not form any meaningful bond with the main characters, remaining a background figure throughout the events.

Masayo undergoes no significant character development or personal growth. She appears only as a supporting suspect and witness, and she does not demonstrate any special abilities or skills beyond her ordinary managerial tasks. Her role serves to illustrate the toxic environment surrounding Juri and to contribute to the list of possible suspects in the murder case.