Well, the world has gone nuts. A disease had spread throughout the world, infecting large amounts of the human population— and even some of the animal population— turning them into zombies... Or worse. It's been about a year since it all started, and it hasn't gotten better.

You're one of the lucky few who have survived, and are currently in a small town, staying in a house. As you sit there on the roof, you spot four boys. They were all prepared; wearing apocalyptic gear and having weapons strapped to their bodies, obviously equipped for danger and such as they kept an eye out for anything.