Katsuko Momose is the founder and president of the Freesia Credit Bureau detective agency. She appears as a stout woman with short brown hair, typically dressed in a white shirt, black bowtie, and dark blue skirt. Her personality centers on a strong work ethic; she is usually too busy to investigate unpaid matters, though she makes exceptions for her longtime friend Yasuji Ban, especially when he brings wagashi, which she enjoys. Despite their friendship, she openly criticizes Ban for reckless actions during investigations, such as endangering his partner Mamoru Suwa.

Her background involves working with Ban to uncover the perpetrators of the New Generation Madness murders and later collaborating with Takeshi Shinjo and Mio Kunosato on the Return of the New Generation Madness cases. Unexpectedly, the Sena route in *ChäoS;HEAd NoAH* reveals she serves as a Debugger and Surveillant for the Committee of 300. In this role, she eliminates "errors," including traitors like Gen'ichi Norose who rebelled against the Committee. Her actions as a Debugger paradoxically align her with protagonists like Takumi Nishijou and other Gigalomaniacs against Norose, despite the Committee's antagonistic goals.

After Norose's defeat and the destruction of Noah II, Momose resumes her role as a Surveillant, using her detective agency to gather information for the Committee without active intervention. At the end of the Sena route, she appears to adopt a baby originally labeled a "cheat code" by the Committee, now deemed an "error" due to its survival, hinting at complexity in her allegiance.

In *Chaos;Child*, Momose and her agency continue operating as detectives and information brokers, assisting investigations into the Return of the New Generation Madness murders. Her deeper connections to the Committee are not explicitly revisited here. Her involvement in *Silent Sky* is not detailed.