David and the others are currently roaming around the border area between the outer area and the inner area. All of them wanted to feel what would be the difference when they would fight Monsters around that place. Until now they already met many monsters who have the ability to kill them but still because of their cautiousness they can win.
David and his group will always avoid any big group of monsters as they know they do not have the capability to fight a big group of monsters. So they would always target a small group of monsters.
So, like this, they came to the area where they saw a group of monsters who were powerful compared to the monsters they had seen earlier. Just feeling the power of those Monsters you can tell they are very dangerous.