Rinko Akaishi is the devoted mother of the protagonist, Kuroe Akaishi, in the manga series Kaiju Girl Caramelise. Her background reveals that she was formerly a biologist who, during her travels, discovered the remains of a kaiju. At this site, she found an egg, which she decided to take home with her, swearing a colleague to secrecy about the discovery. Rinko then proceeded to raise the shapeshifting baby kaiju that hatched from this egg as a human daughter, giving her the name Kuroe. This origin story is supported by visual clues within the story, including a picture of Rinko wearing an archaeologist's hat and the presence of the egg itself, implying that Kuroe may not be Rinko's biological child, though this is not something Kuroe herself is aware of.

In terms of personality, Rinko is characterized as a supportive and protective figure who is fully aware of her daughter's true kaiju nature. She is consistently there for Kuroe, particularly in the face of judgmental people, and understands the struggles her daughter faces due to her uncontrollable transformations. Rinko has a personal fondness for the singer Mayumi Hamasaki, a character based on real-life singer Ayumi Hamasaki. Her role in the story is primarily as a maternal guardian and a keeper of Kuroe's secret. She is the one who eventually confesses to Kuroe that she is, in fact, a kaiju, confirming experiences that her daughter had dismissed as realistic dreams.

A key relationship in Rinko's life is with her former colleague, Koutarou Hibino, who was with her when she found the kaiju egg. While Koutarou does not fully approve of how Rinko chose to raise Kuroe, he acts as a protective uncle to the girl. Rinko's relationship with him becomes more complicated when he starts working for the Japanese government, which alarms her as she wishes for Kuroe and her newly hatched sibling to live happily without interference. There are no notable abilities attributed to Rinko Akaishi herself beyond her background as a biologist.