NK Cell manifests as a muscular female lymphocyte sporting short, uneven black hair that covers one eye. Her typical practical attire consists of a black tank top, green shorts, and boots. She wields a specialized saber that transforms into a glowing purple weapon when activated by Dendritic Cell. Her core biological function involves independently patrolling tissues to identify and eliminate cancer cells, virus-infected cells, and other abnormal cells through cytotoxic actions, operating without prior antigen exposure as part of the innate immune system.

Her personality blends aggression during duties with sarcastic humor and a preference for solitary work, partly motivated by concern for others' safety. She exhibits a competitive yet cooperative dynamic with Killer T Cell, frequently engaging in verbal disputes and physical brawls over jurisdictional responsibilities while fundamentally complementing his immune functions. She displays amusement at Killer T Cell's misfortunes. Her combat effectiveness fluctuates with her emotional state, significantly strengthening during laughter but diminishing under stress or self-doubt.

Key abilities include heightened sensory detection of disguised threats, exceptional combat speed and strength enabling tissue barrier destruction, transmigration capacity for rapid inter-tissue movement, and adaptive memory allowing recognition of previously encountered pathogens for more efficient elimination. Her activated saber serves as her primary weapon during confrontations.

Background elements reveal an unexpected past interest in gothic lolita fashion during her youth, a detail preserved in Dendritic Cell's records that causes her significant embarrassment when remembered. Despite her "loner" reputation among some immune cells, she participates in social activities including Macrophage's tea parties with Eosinophil and Mast Cell, hot spring trips with Mast Cell, and maintains discreet cooperative relationships with Neutrophil and other cells during crises. Her history includes at least one prior male counterpart observed in flashbacks, differing in appearance with blonde hair, long pants, and boots.

In the "Cells at Work! BLACK" spin-off, she retains core characteristics including appearance, solitary patrol patterns, and pathogen-combat duties. Across all appearances, her operational independence remains consistent while demonstrating capacity for coordinated immune responses during significant threats alongside other lymphocytes.