Your day begins before dawn.

Due to certain circumstances, you live within a fortress nestled between two walls erected to protect citizens from a mysterious outbreak that has ravaged the country.

Each day you wake up, fire warning shots from your machine gun, eat MREs, and then settle in for another night. For two years this has been your routine.

But then, everything changes. You rescue a survivor—Satani Kasumi—and shelter her within the fortress.

Despite being someone in need of rescue herself, for reasons unknown, she begins to take care of you. Thus begins a life that is slightly unsettling and strange, yet lively and peaceful all at once...