Shin Angyo Onshi is a Manhwa (Korean manga) series written by Youn In-Wan and illustrated by Yang Kyung-Il.
The main character is Munsu, an Angyo Onshi (ancient Korean law enforcement officers who would expose corruption in local governments, in this story they have magical powers and can summon phantom soldiers and such).
The Power of the Verse
Shin Angyo Onshi is quite an impressive series, bullet - timing feats are common, powerful ki attacks which can range from city block to small city level and armies of demons are also present.
The most powerful character is Aji Tae, a formerly human creature who is an expert manipulator and has very broken powers (for example, he can make you explode just by looking at you). The verse sadly suffers in the durability department, the characters are glass cannons. They lack quantifiable speed feats as well.
Aji Tae's army