Aka Ribbon is a supporting character in the anime Ray, known for her distinctive red hair accessory from which she derives her name. She was one of several children raised in a secretive, isolated facility alongside the protagonist, Kasugano Ray. In this environment, the children often named themselves after their most cherished possessions, leading her to adopt the name Aka Ribbon, which translates to Red Ribbon.

Her background is defined by this traumatic childhood, during which she and Ray were eventually separated. A decade later, Aka Ribbon reappears in Ray's life under mysterious circumstances. She is discovered at the scene of an accident, appearing disoriented and suffering from a broken arm and apparent amnesia, with no memory of her shared past with Ray. Ray brings her into her home, and Aka Ribbon subsequently lives with her, often accompanying the surgeon on patient visits.

In terms of personality, Aka Ribbon frequently presents a child-like and innocent demeanor. This behavior often places her in the role of comic relief, providing moments of levity during the series' heavier and more dramatic storylines. However, this cheerful exterior masks a more complex and darker interior. As the narrative progresses, it becomes evident that her amnesia was likely fabricated from the start. She is eventually revealed to have been sent by the same organization that raised her and Ray, acting as an agent to keep tabs on the protagonist. Her initial mission involved carrying a dangerous, mind-controlling parasite, which she inadvertently spread among hospital staff until Ray was able to surgically remove it.

Aka Ribbon's key relationships drive much of her character development. Her bond with Ray is central, beginning with her apparent vulnerability and dependency, which later curdles into concealed hostility and jealousy. This animosity is largely fueled by her deep romantic love for a man named Koichi. Aka Ribbon is annoyed and pained by Koichi's singular romantic focus on Ray, a relationship she finds particularly disturbing because Ray is, in a genetic sense, Koichi's mother. Her love for Koichi and her resentment of Ray ultimately become her undoing. In a fit of jealous rage, she threatens to harm Ray with a scalpel. In response to this threat, Koichi shoots and kills her, bringing her tragic arc to a close. Regarding notable abilities, Aka Ribbon does not possess any inherent supernatural or extraordinary physical powers; her primary function within the plot is as an unwitting or potentially witting vessel for the biological parasite used by the organization to control others.