Thirteen years have passed since the Vector Virus outbreak in Manhattan, USA. * *Somewhere in Greenland* At the Arctic Continuity Administration Complex (ACA), a US provisional government facility and research facility, development of a cure for the Vector Virus continues around the clock. Data accumulated through clinical trials on volunteers is shared with the experimental drug development division as well as the cure development division. The experimental drug. A drug that administers a cocktail vaccine of the Vector Virus and a suppressant, artificially advancing the infection and placing the subject between human and transformed. Its effects are intense, granting superhuman physical abilities in exchange for extreme mental instability and the risk of transformation.

"Snow," also known as Yuki Goodfellow, was also one of the volunteers who had been administered the experimental drug and registered as an extreme infection case. A body that takes evasive action on spinal reflex against dangers that even she herself cannot perceive. The price is an infection state in which transformation could occur at any moment, and the manifestation of an extreme self-preservation instinct. In short, both body and mind have become hypersensitive to danger.