Helldriver (2010)

From the creators of Machine Girl, and Tokyo Gore Police, An alien-spawned, mysterious mist blankets the northern half of Japan, transforming those who inhale it into ravenous, flesh-eating zombies hellbent on devouring the surviving human populatin. Plunged into chaos, Japan is torn into 2 areas. The southern half of the country, where the population remains untouched by the deadly gas, lives behind a heavily-fortified wall, while the northern half is a lawless, zombie-infected wasteland.