Riko Mikogami is one of the Mikogami twins living in Kamihama City. She possesses one-quarter Animalian heritage, a lineage crucial to her later development. Initially, she discovers a Kirumin compact, enabling transformation starting with a domestic cat form that grants catlike agility, speed, and high jumping. Her Kirumin progression includes accessing a serval transformation in episode 18 and a puma in episode 42. By the series conclusion in episode 50, her Animalian blood activates independently, allowing bat transformation without the device.

Naturally hot-headed and self-centered, she frequently clashes, especially with Ken Inomata. However, she demonstrates genuine care for him during peril, like when trapped together. She exhibits wit and intuition for solving mysteries but struggles academically, particularly disliking algebra. Irresponsible and reckless, she treats the Kirumin more as a toy than a research tool.

Her behavior displays catlike traits, such as chasing flashing objects and a strong seafood preference. Energetic and adventurous, she expends high energy quickly but tires shortly after. She proclaims herself leader of the Detective Club under the alias "The Great Detective Catherine," refusing to abandon anyone needing help. She also has notably poor drawing ability. Her dynamic with Ken involves constant arguments due to shared egotism, yet they maintain a close, mutually supportive relationship.

Her Animalian ancestry originates from her grandmother, Marianne Schönberg, explaining her latent abilities. This heritage risks permanent animal transformation and loss of human consciousness if she exceeds the Kirumin's 99-minute limit. Her quarter-Animalian lineage is fully realized alongside her twin, Rimu, in the finale.