Momoka Sonō is a sixteen-year-old high school student who works as an idol voice actress and musician for the agency Voice Enterprise. She is the daughter of a famous animation director and a well-known voice actress, which positions her as a deeply connected insider within the anime industry from the start. In the fictional anime within the story, she provides the voice for the character Yuzu in the series Millennium Princess x Kowloon Overlord.

In terms of personality, Momoka is outspoken, assertive, and carries herself with a noticeable sense of confidence. She is often described as cheeky and bratty, and the material itself classifies her as a flawed character, rubbing others the wrong way with her direct manner. She does not hesitate to speak her mind, and she shares a certain sharpness with her colleague Chitose Karasuma, which forms the basis for a candid but cautiously distanced friendship. While she can be competitive and seemingly self-interested, she is also practical and understands the professional boundaries of the industry.

Her motivations are shaped by her family background. Having grown up surrounded by successful industry professionals, she carries a natural expectation of success and a clear awareness of how the business works. She wants to advance her career on her own terms, though she is not naive about the shortcuts and politics that come with being a nepotism hire. She values her own autonomy and does not easily tolerate being used as a stepping stone or a decorative face in a project.

Within the story, Momoka functions as one of the main voice actresses in the show-within-a-show and serves as a foil to the protagonist Chitose. Where Chitose is oblivious and reckless, Momoka is more self-aware and calculating, yet both share a lack of humility that makes their dynamic interesting. She is also part of the fictional unit Kohaluna alongside Kazuha Shibasaki, contributing to the musical performances tied to the animated series.

Her key relationships include her interactions with Chitose, whom she treats with a blend of camaraderie and condescension. She also has a working relationship with her fellow voice actresses, particularly Kazuha Shibasaki and Koto Katakura, and her relationship with her mother, Sakura Sonō, is a significant source of tension. When her mother is brought in for a co-starring role using the mother-daughter angle as a marketing tactic, Momoka feels complicated about being used as a publicity device.

Over the course of the series, Momoka shows limited but noticeable development. She begins to confront the pressures and compromises of the industry more openly, particularly around the issue of her family name and the expectations tied to it. She remains largely pragmatic and sharp-tongued, but she also reveals a more vulnerable side in moments where her career choices and personal integrity are questioned.

Notable abilities include her skill as a voice actress, which is competent but not extraordinary, and her musical performances as part of the Kohaluna unit. She is also savvy about media appearances and fan interaction, leveraging her looks and confidence to maintain her status. Beyond these professional skills, she has a perceptive understanding of industry politics and is adept at navigating the tricky social dynamics of the voice acting world.