Momo Shirai is a police officer in the anti-phantom thief department, directly reporting to Dogusaburō Oniyama and partnering with colleague Ginko Kurosaki. Her duties focus on assisting operations to capture the phantom thief Joker and his crew, to which she remains consistently dedicated.

She possesses short blond hair with spiky ends and a fair complexion. Her most recognizable features are her consistently closed eyes and frequently depicted rosy cheeks. Her standard attire is a distinctive pink, white, and black police uniform, usually worn with a matching hat.

Personality-wise, Momo exhibits a peppy and energetic demeanor despite her professional role. While generally more easygoing than Ginko Kurosaki, she maintains a strong commitment to her work and proves an effective team member during Joker heists. She does, however, occasionally prioritize leisure over duty during these operations.

Her background includes a long-standing partnership with Ginko Kurosaki dating back to their school days. Prior to joining the anti-phantom thief department, she served on a special assault team.