What do you mean the mountain city is burning?

This sentence means the forging process of Japanese knives.

"Mountain City" generally refers to the sword used by samurai, referring to the mountain city. When forging "flying burning", the blade was pulled away and ran to the "subway". If it is on the "building", it will become a "building burning".

"Burning blade" is generally called "burning blade covered with soil", which originated in the early Tang Dynasty. Japan has been used to cast swords since ancient times, which is a crucial forging process. Generally speaking, it is to wrap the knife tire with soil and expose the blade part.