Eriko Kaneda, almost universally referred to as Doc, is a central figure in the city of Lux. A first-rate expert in the field of texhnolyzation, she originally belonged to the Class, the elite ruling group living on the Hill above the city, but came to Lux to advance her studies away from the strictures of her former peers. Her expertise is such that she is entrusted by Keigo Onishi, the leader of the Organo, to maintain and improve his own texhnolyzed limbs.

Physically, Doc is an attractive woman with long blonde hair and piercing blue eyes, typically seen in a practical, form-fitting black suit that reflects her work in the laboratory. This outward appearance of calm professionalism, however, masks a deeply complex and obsessive personality. She is cheerful and talkative, especially on the subject of her life’s work, but her sociability masks a profound disinterest in people as individuals. She harbors a deep disdain for the Class and feels little genuine care for the inhabitants of Lux, viewing them not as ends in themselves but as potential components in her grand project. Her driving motivation is not healing but evolution; she sees texhnolyzation not as a medical replacement for lost limbs but as the primary vehicle for the next stage of human development, a means to create a perfect fusion of machine and organism that will allow humanity to transcend its meaningless existence.

Doc’s role in the story is inextricably linked to the protagonist, Ichise. After he loses an arm and a leg, she saves his life by providing him with experimental prototype prosthetics, making him her primary test subject. Her relationship with Ichise is a tangled web of creator and creation, surrogate mother and distant son, and even possessor and possessed. She displays strong possessiveness toward him, desperately seeking him out when he runs away, as he is the vital proof of her genius. The bond is forged in manipulation; to secure his cooperation, she tells him that the cells of his deceased mother were incorporated into his new limbs, a lie she recognizes as the only way to control him. In return for her work, Ichise tolerates her advances, and it is implied he allows a physical relationship with her as payment for her services, viewing her as a kind of surrogate mother figure. Her other significant relationship is with Onishi, which is strictly professional—he provides funding for her research, and she maintains his texhnolyzed limbs, with no personal affection involved.

The trajectory of Doc’s character is one of tragic and total collapse. In the beginning, she is a figure of relative optimism and control, driven by a grand, if cold, vision for humanity’s future. However, her worldview is systematically dismantled. When she finally perfects her research and returns to the Class to present it, hoping to be welcomed back as an equal, she is cruelly rejected. The new ruler, Kano, not only dismisses her but uses her life's work to create the Shapes, monstrous cyborgs that pervert her vision of human evolution. This rejection shatters her purpose. She descends into a deepening depression and alcoholism, frequently seen drinking red wine from a lab beaker as a symbol of her degenerating state. Later, she is asked to travel to the surface world to warn the people there of the coming threat. Upon arrival, she is confronted with the ultimate source of her despair: the surface dwellers have already lost all will to live, having given up on survival entirely. In this empty paradise, she realizes that her entire life's work on texhnolyzation as an evolutionary trigger for a species that has already chosen to die was utterly futile. With no purpose left and her meaning erased, she loses all hope. In her final appearance, after Ichise leaves to return to Lux, it is strongly implied that she commits suicide, drowning herself in a bathtub. Though she later appears as a shadowy vision in the final episode, this is presented as a spectral echo rather than a physical return, activating the last reserves of power in Ichise’s limbs as a final, ghostly act of her will. Her notable abilities lie entirely in her scientific genius, her mastery of texhnolyzation, and her skill as a surgeon, all of which ultimately prove powerless to save her from the nihilism she tried so hard to overcome.