Niko Urushizaki is a character who appears in the live-action film adaptation of Cells at Work!, serving as one of the human hosts whose body provides the setting for the story. She is a high school student living with her single father, Shigeru Urushizaki, after losing her mother at a young age. Niko is defined by her sincere, responsible, and health-conscious personality. She maintains a balanced diet, exercises regularly, and follows a disciplined daily routine, which creates an ideal environment for the cells inside her body to work happily and efficiently. Her motivations are largely centered on caring for her father, who is her only remaining family, and managing their household despite his lack of discipline. She also harbors a quiet romantic interest in her upperclassman at school, a detail that adds a layer of personal emotional depth to her character.

In the story, Niko represents the contrast between a healthy and an unhealthy body. While her own body is a model of wellness, her father's body suffers from the consequences of smoking, excessive drinking, and poor diet. Her role is primarily that of an observer and emotional anchor for the audience, as the narrative alternates between the cellular world within her and the human world outside. The cells inside her—such as the red blood cell and white blood cell—work contentedly and without the extreme strain seen in her father's body. Her key relationships include her father, for whom she acts as a caretaker and moral counterbalance, and her school senior, who represents a normal teenage concern that affects her emotional state. The development of her character is tied to the growing health crisis affecting both her and her father, as well as the emotional strain of confronting potential loss. She possesses no supernatural or unusual abilities; her notable trait is her commitment to a healthy lifestyle, which directly influences the well-being of the cells within her.