Created in 2140 through genetic engineering by the Central Government, 044 is a clone soldier designed as a combat tool. Modified using the Hemophage Virus, she possesses superior strength, agility, and combat proficiency, ranking as the government's most elite operative. This modification accelerates her physical degradation, resulting in a severely limited lifespan.

Deployed on missions to eliminate the Phage rebel group—infected with the same virus—044 infiltrates their ranks under orders. During an assignment to assassinate Phage leader King, she encounters Phage soldier Luka Bloom. Defying direct commands, she cannot kill him and instead rescues him from injuries. This act brands her a traitor, making her a target for both the Central Government led by Daxus II and the Phage forces.

Her rescue of Luka triggers a psychological awakening. Accustomed to obedience, she begins experiencing unfamiliar emotions and contemplating existence beyond her programmed purpose. This introspection compels her to flee Neo Tokyo with Luka and her guardian, Dr. Garcia, who abandons his government position to aid her. During their escape, she grapples with newfound autonomy, questioning her identity and the world beyond government control.

Her journey reveals hidden truths about the Central Government, including Daxus II's own clone origins. She allies with former adversaries like Sakuza (Clone 6030), a defector from the government's clone forces, to challenge the regime. Ultimately, she returns to Neo Tokyo to confront the government directly, participating in a final assault on their headquarters. In the climax, she sacrifices herself to ensure the mission's success, dying as the building is destroyed. Her actions catalyze the government's downfall.

After her death, Luka survives his injuries and recovers under Dr. Matilda's care, while Garcia continues living with the legacy of her choice to defy her creators.