Natural Killer Cell is a female lymphocyte with a muscular, fit physique. She has short, uneven black hair covering her right eye and wears a black tank top, green shorts, and boots. Dendritic Cell activates her, causing her standard saber weapon to crack and reveal a purple lightsaber, enhancing her combat capabilities.

Her personality is sarcastic, and she prefers working independently, partly to protect her friends from danger. During duties, she exhibits antagonistic and aggressive tendencies, including threatening normal cells when necessary. She maintains a recurring rivalry with Killer T Cell, characterized by frequent bickering over task ownership and physical confrontations; she finds amusement in his misfortunes.

Functionally, she specializes in identifying, tracking, and eliminating cancer cells, viruses, and infected cells. She patrols freely across tissues, using heightened senses to detect disguised threats. Key abilities include cytotoxic attacks to eliminate aberrant or healthy cells at her discretion; transmigration allowing unrestricted movement through tissue barriers for rapid target engagement; expert proficiency in wielding her saber as a primary weapon; adaptive memory to recall attack patterns of previously encountered infected cells for efficient elimination; and enhanced combat capabilities enabling her to break tissue walls during fights and handle tasks equivalent to multiple Killer T Cells single-handedly.

The spin-off *Cells at Work! BLACK* features a version of Natural Killer Cell with identical attire and abilities, operating within that narrative's distinct, stressful physiological setting. Her operational role remains consistent across depictions: an agile frontline defender utilizing rapid response and memory-based tactics to suppress infections and malignancies.