"This stone has a hard texture and is made of the same material as the city gates. It is immune to any spiritual power attacks. Of course, if you want to forge or refine it, you cannot use spiritual power either. I suggest using a Different Fire or extremely hot naked flames."
As he spoke, the resident official pointed to a fiercely burning stove nearby.
"When we used this material to build the city gates, we burned a great deal of combustible materials."
Chapter 21