Aria

Aria is an Angyo Onshi who possesses the one-horse mahai. In his quest, he is accompanied by his unnamed Sando and Bang Ja. Before the events in Shin Angyo Onshi, he was already deceased.

Gaiden - Bang Ja Story
Bang Ja's story begins with Aria confronting a corrupt officer. Showing his one-horse mahai, he shouts "Angyo Onshi no Odemashida!", signaling a group of soldiers.

After a job well done, Aria's team sets out for another journey. One night, Bang Ja went outside and heard someone crying. Curious, he checked the source of the sound. He found a girl praying at an altar. The girl told him that her father couldn't pay his debt to a wealthy man, so he was taken away. Bang Ja sympathized and told her that an Angyo Onshi will come to help her father.

Unfortunately, upon telling Aria about it, he simply told Bang Ja that it is impossible. Their investigation of the town where the girl's father was held had already been completed and no trace of corruption was found. With no other choice, and no way to keep his promise, he stole his master's mahai, and went with the girl to the place where her father was held.

Due to Bang Ja's recklessnes, he had forgotten that the mahai summons assistance from Jushin Administration, but one must request it first. Thus, the mahai is rendered useless. Not knowing it, he still confronted the officer and showed the mahai, ordering him to free the girl's father. Unexpectedly, the girl's father showed up and embraced her daughter. Much to Bang Ja's surprise, the father stated that he was working to pay off his debt by doing some work. Thanks to the officer's kindness he would be out of debt soon.

Bang Ja was then informed that the officer was  Razor,  the minister of Jushin's internal affairs who was in charge of appointing Angyo Onshi. As he never seen Bang Ja, he knew that Bang Ja was a fraud and must be punished.

To save Bang Ja, Aria came and told Razor that he was the one to blame. He claimed responsiblity for all Bang Ja caused because he "gave" him the mahai. Bang Ja knew that Aria was protecting him by pinning all the blame to himself. Razor claimed that, since it was a serious crime, a punishment was necessary. Razor chose Tae Hyung, a torture that will unleash a great pain in the victim with single lash of his whip. Bang Ja knew that he should be the one punished and tried to save his master. Aria calmed him, telling him that he was glad they would be forgiven just with one whip lash. Though the torture gave Aria incredible pain and nightmares, he forgave Bang Ja. The two grew closer as they were able to trust each other more than ever.

Death
When Jushin's fell, Aria's one horse mahai became useless. Though powerless, he still wanted to fight corruption. Before confronting a certain officer, he abandoned Bang Ja without warning. Accompanied by his sando, he tried to arrest the corrupt officer but to no avail. Failing in their mission, they were later executed.

Around a month after that, Bang Ja saw their severed heads and later came to know the whole truth of what Aria had done. Seeing their efforts to free the world of corruption, even it cost their lives, made Bang Ja swear to set of on another journey, to find another Angyo Onshi to serve, thereby continuing his dead master's efforts.

Trivia

 * Aria is the only known Angyo Onshi who possessed a one-horse mahai.