High-level martial arts: Long spear with black flames to suppress demons.

[Genius + Overwhelming Victory + Slice of Life + Thrilling Read] [Rating just released, will rise]
"The Provisional Regulations on the Management of Demons in the Eastern Empire stipulate that anyone who crosses the border and injures others shall be killed without mercy."
In a dark alley, Shen Chang'an, an 18-year-old high school senior, stared at the monster before him and recited the regulations with a blank expression.
"Where did this student come from? Kill him!"
Shen Chang'an sighed and casually smashed the black wooden guitar case on his back onto the ground.
There was no guitar inside, only a heavy, black nunchaku weighing over 100 pounds.
What provincial capital prodigy? What millennium-old demon? What monstrous monster?
Since demons roam freely in this long night and the rules have collapsed.
Then I, Shen Chang'an, in the name of the Lord of the Night, will use my gun and black flames to teach the demons some rules!