Rimu Mikogami is one of the twin sisters in the Mikogami family, distinguished by indigo hair and blue eyes usually hidden behind large glasses. She attends elementary school with her sister Riko and friend Ken Inomata. Her primary Kirumin transformation manifests as a rabbit, associated with the color green, granting enhanced hearing and speed in Costume Mode. She carries an apple-shaped camera and notepad, tools reflecting her role in the school newspaper and passion for journalism.

Rimu learns animal communication from her mother, aligning with her family's connection to animals. Her personality blends shyness with perceptiveness, becoming significantly more expressive when not wearing her glasses. Interactions with Tamao Kijima, who harbors a crush on her, drive character development; his glasses frequently crack in response to her attention or concern. Her abilities evolve beyond basic transformation, including turning into a platypus and achieving the "Kirubara effect" for larger animal forms.

Her heritage reveals she is one-quarter Animalian, a trait shared with her sisters, which enables her to transform into a bat without Kirumin devices in the series finale. This lineage connects her to the Hatori family, identifying Kanon Hatori as her cousin. Rimu faces emotional turmoil when Ken Inomata exceeds the 99-minute transformation limit, risking permanent loss of human consciousness.

She actively participates in the Detective Club's investigations, utilizing her Kirumin abilities to gather clues and understand animal perspectives. Her grandfather, Yuuki Mikogami, is later revealed to have been trapped in turtle form under the alias Doctor, adding familial depth. The series concludes with Rimu's extended family reconciling as Misa and Kanon Hatori return to Vladonia while the Kibagumi members remain in Kamihama.