Mine

"Ghost Spirit Crystal?" Ling Han asked.

The woman nodded, "That's right. When the strength of our souls has advanced into the True Self Tier, killing ordinary Yin souls would no longer be able to strengthen our souls. We would only be able to kill True Self Tier Yin souls, or… use Ghost Spirit Crystals."

"And then?" Ling Han asked.

The woman was neither too fast nor too slow, "There are very few Yin souls of True Self Tier, and they are also very hard to kill…"

At this point, she paused. This did not seem to be applicable to Ling Han. Just now, this guy had practically killed a Yin soul of consummate True Self Tier. He could not be measured in terms of common sense.

She continued, "So, if one can refine the Ghost Spirit Crystal, it would be much simpler."

Ling Han smiled, "You know where there is a large number of Ghost Spirit Crystals?"