Zheng Que spent the night in the alchemy furnace again.
Apart from costing him an Imperial Edict, the recovered Qing Li was none the worse for wear.
With the alchemy furnace concealing the aura of a living person on him, they made it through the night in peace.
As soon as day broke, Zheng Que set off again with his two Ghost Servants.
The sun rose in the east and sank in the west. Time slipped by unnoticed.
Another day passed this way. Ku Lan's cultivation reached the fifth level of Tongue-Pulling Hell. Two days after that, Qing Li's cultivation reached the sixth level of Tongue-Pulling Hell.
After several days of testing, Zheng Que gradually confirmed a theory he had come up with earlier...
The Yin energy of every ghost slain by his Ghost Servants, or slain by his own hand, flowed into the Underworld.
The Underworld could absorb this Yin energy and, through the "Command Character" in his palm, feed it back to his Ghost Servants.
However, the Yin energy from ghosts slain by Qing Li could only be fed back to Qing Li.
Likewise, the Yin energy from ghosts slain by Ku Lan could only be fed back to Ku Lan.
Therefore, no matter how many ghosts these two Ghost Servants killed, they could only receive their own share of the Yin energy...
Only ghosts personally slain by him, their master, could provide Yin energy for all his Ghost Servants. But there was another limitation: each Ghost Servant could not fully absorb all the Yin energy he fed back to them.
That was why, the first time he raised Ku Lan's cultivation, she advanced only from the first level of Tongue-Pulling Hell to the second.
At the time, Ku Lan had only just become his Ghost Servant and