Olivia was not the only one that was engaging in the fight. Instead, Adam and Sarah were also attacking. It was just that they were supposed to fight against several hundred members of the dark race.
But, it was a good thing that although the members of the dark race possessed a number advantage, when it came to the strength, they were not that much. So, with just a single attack from each of them, they were able to eliminate about 10 or 20 of them at the same time.
Both Sarah and Adam possessed incredible strength, with the both of them possessing SS grade professions. As for Sarah, she was the complete nemesis of the members of the dark race considering that she possessed the light element.