Kamiyagawa: "By the way, Uncle Yuuki, have you ever heard of the ashes of war left behind by heroes after they die?"
"Uh-huh, of course I have. Why?"
The ashes of war are relics left behind by great human heroes after their demise. The special operations room's predecessor was the Yin-Yang Bureau, which is a large organization with a long history; it wouldn't make sense for them not to have seen such a thing.
"It would be best to forge firearms with the ashes of war."
On this point, Kamiyagawa chose to be somewhat honest.
His relationship with Uncle Yuuki was both mentor and friend, after all, they had fished together, eaten together—a bond forged through shared experiences.
Moreover, the earlier question from Kamiyagawa about his "master"...
Truth be told, Yuuki Masamune's words carried a significant amount of inducement.
Acknowledging his apprenticeship to a ghost god was the best, most reasonable, and most acceptable explanation for his abilities to others at the moment.