A woman who works on the local police force. She is fascinated yet terrified of Fran. In chapter 13, she goes under a forced surgery to allow her sense of smell to be heightened. She uses this power to find and kill all of the accidental duplicates of Youka to which she reluctantly complies with, otherwise the world would be overrun with Youka clones as they don't stop multiplying until Fran inhibits the original Youka's genes.
In chapter 44, numerous clones are made of her against her will through asexual mitosis. Over 1,100 clones are on an island anticipating Gavrill in an attempt to hunt her down. They are easily eviscerated by Gavrill but Fran's plan was to allow them to be fodder in order to let Gavrill cool down and end her rampage.
In chapter 48, she organizes a meeting with Fran to discuss bizarre cases of missing people and suspects a cannibal is responsible, and asks Fran is she knows anyone who could be such a culprit. Fran discovers that all the victims are related through having the same autoimmune disorder, Laocon's Disease. Using donor waiting lists to find a potential suspect, the police arrest 22 year old Nogizaka Erika. Rumiko allows Fran to interview Erika as she hasn't said a word since being caught and hopes Fran can open her up. Fran deduces that Erika has oral tolerance to antigens and thus, began eating infected organs of those who also had the disease to build up an immunity. Erika reveals her sad childhood to Fran and Rumiko about her neglectful mother, her early onset with the disease, eating her own skin to stave off the symptoms and cannibalizing her mother which lead to her feeling better but in reality she was weakening her immune system from fighting off a cancer that had now become a tumor. Rumiko is sympathetic to her plight of survival but still cannot let her go as she's killed and eaten so many people. Fran helps her with a multiple organ transplant, which works to heal her body, and she's been kept out of jail due to some possible deal with Rumiko but Fran reveals to her staff that while Erika's other organs are great, her brain has become deformed due to prions from her cannibalistic ways.
She appears again in chapter 54, being tasked to find out about a Mr. Matsumae Tadashi who has retreated from the business world and bought an island where he supposedly runs human experimentation trials. She asks Fran for help in learning about the man and going to spy on him as he's been buying scores of artificial bodies in the past months. The duo believe Tadashi has been buying artificial bodies and bought the island to relive his teenage years as he is seen wearing a school uniform and walking with others towards a high school. Offended at first, he was about the threaten to kill them but Fran interrupts that she's impressed he actually gets to live out his dream and now embarrassed, he offers to give them a tour. Rumiko feels an overwhelming sense of nostalgia and begins crying as Tadashi feels they are kindred spirits who never truly got to experience their teenage years due to studying too much instead of being more social. It quickly turns into a pseudo-harem for Tadashi as every girl, (classmates, teachers, etc...) is seemingly into him, making him lunch and starting conversations with him, and Rumiko begins to freak out as she notices all the girls look like her to which Fran reveals all the artificial bodies she sold to him were of her clones. She is horrified and seemingly goes mad at the sheer amount of work Tadashi has gone through to live his dream life with her clones who have various jobs and teams of writers to plan out their daily dealings with him. It also seems that Fran has left her behind on the island as Fran is on a speedboat and a film crew finds Rumiko and can't tell where she belongs so they send her to get her mind wiped.
The next couple of days, Fran is watching the film crew organize Tadashi's day; his walk to school, his school day, his walk home, enemy encounters, ect... A bandaged person has escaped after having heavy cosmetic surgery and begins killing various "characters" like sister #11, free loader #8, classmate #32 before approaching Tadashi on his walk to school with an axe and killing all his followers gruesomely, shocking Tadashi as he never approved of gore but he seems to think it's still scripted and believes the person to be infatuated with him as they protect him from Fran's new monsters. It is revealed that the person is Detective Rumiko Kuhou (or at least a more aware clone of her), and had surgery to look like a bug as the crew wanted a monster girl actress to use for Tadashi's after-school battles. A sniper team shoots her down before she can kill Tadashi but she later wakes up to him handing her flowers as he has actually fallen in love with her. Fran leaves her behind on the island again as she is on a speedboat heading back to the mainland.
Rumiko appears again in chapter 59, with her face back to normal, investigating the death of 16 year old student Hotaru Miyake at Fran's and Veronica's school. She notifies Fran that Veronica is independently searching for Hotaru's killer as the police are about to call off as there's little to go on. Unbeknownst to her, Gavrill reveals to Veronica and Fran that Hotaru's death has a lot of men involved, including the police, which is why there's little investigative work being done. It turns out Hotaru has requested Fran inoculate her with highly virulent gonorrhea spreading bacteria which has infected numerous men, including the school's boys' sports teams, several teachers, the school's principal, police officers and politicians.
She is mentioned in chapter 60 after Fran-M's work at a city hospital becomes marred due to bribes and easy going policies of signing anything. She has received documents that clear Fran of any wrong doing and to settle affairs with the insurance companies.
In the final chapter, during Fran's oxygen deprived dream, several clones of Rumiko appear for Fran's party.
She has over 1000 clones made of her, which Fran has been selling worldwide.