In the summer of 202X, a crisis befalls the majority of demons who have been absorbing human souls to fuel their magic. As more and more humans become more demonic than demons, there's no longer any need to sell their souls for demonic help. To overcome this employment crisis, demons prepare to change careers(?) into "mongma," capable of absorbing human energy without human consent. (Main character) Upir is no exception, but it's not as easy as he thinks. Eventually, (Main character) Cheol-Ho, a detective who is completely blocked by Upir, who tried to become a mongma through illegal means, appears...

(Source: Lezhin, translated)

Note: Includes three extra chapters.