Blade of the Phantom Master

Blade of the Phantom Master takes place in the fictional land of Jushin, modeled after feudal Korea. In Jushin, there once lived secret government agents called the amheng osa (or angyō onshi in the Japanese version), who traveled the countryside in disguise. They were charged by the king with finding and punishing corrupt government officials, and bringing justice to the country's citizens. At the start of the series, Jushin has been destroyed, fractured into numerous fiefdoms and kingdoms, many of which are ruled by corrupt and tyrannical warlords. Blade of the Phantom Master follows the adventures of one of the remaining amheng osa, Munsu, as he continues to wander the countryside and deals with the chaos caused by Jushin's fall.

(Source: Wikipedia)