After the destruction of Mother Base, surviving soldiers of the Militaires Sans Frontières have somehow been transported to an alternate universe. This nightmarish world is populated with crystalline zombie-like entities known simply as "creatures" and with no contact with the outside world, the Mother Base soldiers much fight for their own lives. Materials and debris from Mother Base can be salvaged and other survivors show up as the lost soldiers form their own fortress to defend and protect themselves from the "creatures" while trying to find a way to return to the outside world.
—J LeGault