The world was invaded by creatures, people built twitches surrounded by giant walls to protect themselves, but for an unknown reason, creatures all over the world broke through the walls. It is not known how they broke through. Our duty is to kill the creatures in the cities and make the cities usable again. It was developed using creature biology and has the only effect on creatures. We can divide the enemies in two with our weapon, the blood sword, but we must be careful, the blood sword has its limits.