In 2203, the "Red Fog Virus" raided the "Pacific Union Metropolitan Area". Within 72 hours, tens of millions of people mutated into flesh-eating zombies. The city was shrouded in thick blood-colored fog. The only escape route, "Arkport", was blocked by "Iron Zombies" that had evolved the ability to devour metal. Shen Ye, a former member of the special mecha unit, encountered an ambush while escorting his sister to escape. The mecha was damaged and her sister disappeared. In desperation, she activated the military's top-secret "Protocol Zero" - a set of semi-biological mecha "Scarlet" that can be deeply linked to the brain's nerves, and gained the ability to "virus synchronize". He drove a mecha alone through the red mist, fighting against the ever-evolving zombie army and the black market forces coveting "Protocol Zero" while searching for traces of his sister. However, he gradually discovered that behind this disaster, there were dark transactions between the military and giant corporations.
