Eriko Kaneda, almost always referred to as Doc, is a scientist and medical specialist who possesses an expert-level understanding of texhnolyzation, the process of replacing human limbs with advanced mechanical prosthetics. Her work is her primary obsession, and she views texhnolyzation less as a remedial medical treatment and more as a crucial step in the evolution of the human species. Doc is originally from the Class, the mysterious and privileged rulers who live on the Hill far above the decaying underground city of Lux. However, she was forced into exile due to ideological differences with its new leader, Kano, and now resides in Lux where she continues her research, funded by Keigo Onishi, the head of the Organo crime syndicate.

Doc has a striking appearance, characterized by long blonde hair and piercing blue eyes. She often wears a form-fitting black suit and maintains a demeanor that is generally cheerful and talkative, especially when discussing her work, though this outward geniality masks a deeper, more obsessive nature. She holds a profound disdain for the people of the Class but also lacks genuine care for the citizens of Lux. Her singular motivation is to perfect her research and create the ultimate form of texhnolyzation that would completely fuse with a human, a goal she believes will prove her genius and earn her reinstatement among her former peers. This ambition makes her a highly rationalistic and pragmatic individual who sees little value in emotional or symbolic acts.

Doc's most significant role in the story is as the creator and primary caretaker of the protagonist, Ichise. After the young fighter loses an arm and a leg, Doc saves his life by fitting him with experimental prototype prosthetics. From that point forward, she treats Ichise as her prized test subject, referred to as her masterpiece. Her relationship with him is complex and multifaceted; while it begins as a purely professional, clinical arrangement, it evolves into a form of possessive attachment and even romantic infatuation, though these feelings are largely one-sided. She sees in Ichise a powerful will to live that she finds compelling, and she seeks to control and guide him. In one notable instance of manipulation, she tells him she incorporated the DNA of his deceased mother into the circuits of his new limbs to ensure his acceptance of them. Her relationship with Onishi remains strictly professional, built on a mutual understanding where he provides funding and resources for her research in exchange for her medical services to maintain his own texhnolyzed limbs.

Throughout the narrative, Doc demonstrates notable abilities beyond her medical expertise. She is highly skilled in the science and application of texhnolyzation, creating advanced prototypes that push the boundaries of the technology. She is also clever and maintains a cool composure even in threatening situations, such as when she is pinned down by an enraged Ichise. Her development arc is one of gradual emotional and psychological collapse. Initially confident and driven, she suffers a major defeat when she presents her finished research to Kano, only for him to reject her and seize her work to create monstrous "Shapes". This rejection sends her into a deep depression, and she begins to drink heavily. Later, after being asked to travel to the surface world to warn people about Kano's plans, she witnesses the apathetic, ghost-like existence of the surface dwellers. Confronted with the pointlessness of her life's work in the face of humanity's resignation to nihilism, she loses all hope and purpose. After her final encounter with Ichise on the surface, she is strongly implied to have committed suicide by drowning herself, though her spirit or a shadow of her appears in the final episode to activate the last of Ichise's power.