Here’s What The Butterfly Dream Manga is About:

The age old fight between grim reapers and demons
Reaches its head in the heart of Modern Seoul!

Jangju (the protagonist), who had inherited the family business and was destined to become the head of the family of exorcism, was addicted to the incident and was excommunicated from the family. He was hired by GVA, a charitable agency, and walked the path of an amateur exorcist.