The Primordial Beast Hunters were not wrong when they assumed that Hei Gou was burning all his energy to be able to increase his speed.
They had, however, underestimated his willpower.
"No!" Xue Wei called out in despair when Hei Gou picked up in speed. "Don't do it! We can escape without you burning your blood essence!" he said in panic, but Hei Gou did not reply and instead pushed himself harder.
A red mist had started to appear around Hei Gou. He was exhausting all his energy for the sake of fleeing. Every single ounce of energy in his body was being squeezed out so that he could fly faster.
Xue Wei was filled with fear. Blood essence was something that should not be burned unless one was in a serious life-or-death situation. When one burnt their blood essence, one would be weak for a time afterwards until the depleted blood essence was restored.