"Kuiyi Stone? Kui Mountain's Doubtful Stone? What a bizarre name." For a moment, I couldn't think of how to explain the thing.
Sana, however, thought for a moment before saying, "I found a stone tablet earlier. It had an introduction written on it. The name Kuiyi Stone comes from the meaning of obtaining the Kuiyi Stone from Kui Mountain. After refinement, it forms something called Sinking Heaven Stone. According to legend, even the tiniest bit of this material weighs over a thousand jin. Its weight is such that it can sink even what should never sink, allowing it to sink all beneath heaven. So when used to refine weapons, adding just a little powder to an ordinary weapon makes it indestructible. That's why even at Mu Immortal Continent's largest markets, it is auctioned by the powder grain. Of course, refining Kuiyi Stone into Sinking Heaven Stone isn't easy. Apparently, an entire square of Kuiyi Stone can produce only a tiny bit of powder."
"Then these crystals..." Curious, I released a pile of Kuiyi Stone that I had obtained from underground.
Sana picked one up and weighed it in her hand before saying, "This is Kuiyi Stone. Although it is already incredibly heavy, it hasn't been refined into Sinking Heaven Stone. If the refinement succeeded, even a piece this large probably couldn't produce a speck of dust. They say the refining method is a closely guarded secret. Even the refining tools have to be made with Sinking Heaven Stone, so no one knows how to refine it."
"It seems Sinking Heaven Stone has probably vanished even from Mu Immortal Continent. We've found their ore vein—we've really struck it rich. These Kuiyi Stone tools are merely mining tools, which shows just how outrageously difficult it is to mine the stuff." I smiled.