Munsu's unwanted but good-intentioned servant. Once the servant and apprentice of a first mahai onshi, his former master released him from service after Jushin's destruction. When his master and his sando were later killed in a rebel uprising against a corrupt lord, Bang Ja began roaming the country as a thief. He believes that angyo onshi should be virtuous and heroic, which is why Munsu's behavior often shocks him.
He is a third-rate Magician who summons animals to do his bidding, and he deeply takes his role as a Bang Ja seriously. This often leads to his being manipulated and bullied by Munsu, who often beats him or sends him on insane/impossible errands.