The demons of chaos, alternatively translated as chaos gods or chaos monsters, are legendary entities in the Monster Girl Encyclopedia world that are sealed away in the deepest part of the sea. Only mentioned briefly in Monster Girl Encyclopedia I, their mystery and alleged power nevertheless make them frequent topics of interest.
Wandering Scholar relates the tale that, in ages past, the demons of chaos and Poseidon shared dominion over the sea. But in the age of the former Demon Lord, a war involving the demons led to them being sealed in the abyssal depths. Even today, Poseidon's power and influence doesn't stretch to the deepest parts of the sea. Although the demons of chaos were naturally male and female, they are "kin to monsters", so Wandering Scholar expects that the current Demon Lord's monster-to-monster girls sorcery will have turned them into all-girl nymphomaniac part-succubi too. But no-one has ever been down to the sea floor to see for sure.
The strange, subterranean mindflayer monsters are suspected of being associated with these demons, possibly preparing the world for their masters' return by recruiting human thralls. The Shoggoth's profile confirm that they've indeed become women and get human husbands.
The sea's way of life (MGE-1)
The deep layer is even further towards the bottom of the sea. It's also called the deep sea. It is even further towards the bottom of a giant hole opened in the sea. No light reaches beyond this point. Also, it's a place beyond the extent of Poseidon's rule. Normal monsters and humans never go near it. According to legend, in the age of the former demon lord, wicked demons of chaos who possessed a power that was even greater than that of the gods existed there at the bottom of the sea. At the time, Poseidon was still one of the divinities ruled by the chief god, and the rule of the sea was split between her and them. It is said that the demons of chaos were sealed in the deep layer after a war, and even now, the demons of chaos are biding their time to make a come back and once again reclaim dominion over the sea. Those who sunk into the depths of the sea, male and female, are also kin to all monsters, so they've probably assumed the female form, and had their thought patterns changed accordingly, but no one has ever been able to confirm it, and the truth of this is uncertain.