Taehee explained it saying that they are the master of the old exorcism agency. They are able to drive out evil spirits, kinda connecting earth and what's next. Wearing a mask known as "the four golden eyes", they can see the name inscribed on a soul and if that name is repeated three times, be it a ghost or a human, that being will vanish from the world. So in chapter 38, Tae convinced mc to help him out getting on the top of the agency, and in exchange he would "kill" him with the mask
Responding to human requests, the "homeland" sent a god called Bangsangsi down to earth to help humanity and restore order between humans and demons.
Bangsangsi helped people spiritually and founded the first exorcism society in the imperial palace aka the Narye exorcism agency. After completing the mission to help people, Bangsangsi intended to return to heaven but was prevented from doing so by the people. To reassure them, he left behind a mask called the Four-Eyed Golden Mask. This mask represents Bangsangsi, and the person who receives it is considered his embodiment, revered and respected by the people, and wielding the power of life and death through the mask. Only a chosen person who will have the mask and become the next Bangsangsi embodiment.
In the modern day, the Director of the Narye agency is not Bangsangsi. That's why Taehee uses Bangsansi as a attack weapon against the Narye agency.

who's bangsangsi again?