Reiko Haga, 18 years old and born on October 31, possesses striking violet hair, purple eyes, and stands 165 cm tall with measurements of 82-58-82 cm; her blood type is A. She works energetically at the cosplay café Cos.Mix alongside friends Miho, Mayu, and Yuka. Reiko's passion for cosplay is an infectious zeal, uplifting everyone around her. She meticulously crafts all her costumes by hand and deeply immerses herself in her favorite roles. Reiko holds the artistry of cosplay in high regard, becoming notably serious when confronting those who disrespect it, especially the "Cameraboys" who take invasive photos without consent.

Within the manga, she actively mentors Mizuki Takase, imparting her knowledge of costume creation and performance techniques. She respects Kazuki Sendō's dōjinshi work and expresses a specific wish for him to create shounen ai content. Reiko's experiences function to promote cosplay culture, highlighting its creative and communal aspects while demonstrating dedication to hobbies and the balance between fandom enjoyment and personal boundaries.