Rumiko Nonaka, the mother of Rika and daughter of Seiko, is a famous model, and constantly pushes Rika to worry more about her appearance, taking her to camera tests and buying "girly" outfits for her to wear (all of which Rika would push away angrily). When the tamer enters the Digital World the first time, she told her grandmother, but not her mother.

Just before Rika's battle with the D-Reaper, Rika's mother buys Rika a T-shirt with a full heart on it to replace the broken-heart one Rika usually wears. She says it is for good luck, and has bought a pink version of it for herself. Rika is touched and smiles at her mother before leaving. She also helps some of the other parents prepare a meal for the children and digimon before the fight.

By the beginning of Dimensions, her relationship with her daughter began to fray once more as she becomes distracted by her work again. When Rika leaves in anger for the Digital World to retrieve Renamon, Rumiko realizes that she is once more risking the loss of her daughter because of her career. While she would never become the perfect mother, she strives to be at least a better one.

When the universes collapse upon each other, she also gains Kristy Nonaka as her daughter. She is unaware that she didn't have both daughters originally because of the collapse. Rumiko is fairly young to be a mother of two, just as Seiko is young to be a grandmother (and later, a great-grandmother). This is because she married Kiyoyuki Nonaka at a young age and later they split up.

While unhappy with the idea of Rika being pregnant in Book Six (she feared history repeating once more), she was determined to be supportive of her daughter. In Book Seven, she was forced to flee a photo shoot with Mimi and Palmon after Rayleigh Thompson accused her daughter, Rika, of murdering the Prime Minister and sent armed forces to gather the tamers. They managed to escape to the park, evade their attempts to trap the group there, and fled to the safety of the Digital World.