There was still quite an amount of spirit stones that Lu Xuan took from the Special Task Force. They were stored in his Coiling Dragon Ring. As such, he had no fear of running out of stones when furthering his training.
Furthermore, that place he was at was the ancestral land of the vampires—a place filled with blood energy.
All that blood was no longer mere blood after being refined for ages; the blood had become flowing energy.
Other creatures had utterly no way of absorbing such refined energy, as they would only end up being overwhelmed.
But then again, Lu Xuan, who had been a Celestial Lord in his past life, had none of such problems.
Lu Xuan knew all too well of the physiological makeup of the vampires. As such, he was able to quickly create a way of absorbing blood energy like the vampires, based only on what he knew about them.
Those techniques were known as the "Sutra of Blood."