Nesk Company is a demon organization in the Underworld that deals with smuggling and other illegal trading. They have their headquarters based in the 1st Demon City of Korun, 4th Floor of Hell. Their business runs mainly on the smuggling and trade of souls, and hires many skilled Soul Hunters to capture and provide the company with souls. Representative Milon had once stated that their daily sale had exceeded 1 million souls per day, and also that they have achieved monopoly in this trade. It also suggests that Nesk may not be the only organisation that deals in the trade of souls. Prior to the Witches arc in the story, Nesk also made dealings with the Witches, and were able to obtain the potent and powerful potions that only the latter create.
Besides smuggling and trading souls, Nesk Company has been experimenting with artificial bodies that demons possess, creating many powerful and impressive weapons and bodies for demons, such as the enhanced arm Milon given to Gilgath to battle Mephistopheles, Kadiran's modified body that uses souls as bullets, weapons crafted from Beelzebub's bone and also imbuing that bone into a demon body.
They also made deals with the Supreme Witch to help her complete her daughter's research into hybriding their bodies with that of demons, whilst betraying her clan in the process, and causing a mysterious "illness" that killed several clanswomen for her own personal gain. This agreement stated to allow even the forbidden potions of the witches to be accessible by the demons which in the end was thwarted by Shi-Hun and company.