The Order of the Chief God, more commonly known as The Order, is the main anti-monster organization in the Monster Girl Encyclopedia world. Part crusading religion, part military superpower, and part world government, the Order holds sway over the vast majority of the world's human population; and within the Order, worship of the Chief God is practiced by the vast majority of the people  (although sects devoted to lesser divinities like Eros and Ares are accepted). The Order is reviled by monsters and their sympathisers as a great evil, but its doctrines are largely benign: that people should live temperate, virtuous lives of kindness and charity - just not kindness and charity to monsters .
Not much information exists on the internal organization of the Order, although there are a few details available. A dedicated military arm called the Order of Holy Knights is referred to as "the clearest symbol of the Chief God's authority" ; both Wilmarina Noscrim and Mersé Dascaros were members.
At the top of the Order's human hierarchy sits a Pope, and there are also living saints . Final authority obviously rests with the Chief God herself, who may make her will known by speaking to oracles, such as Sasha,  or sending angel messengers directly. The gods also sometimes send their angels to help church expeditions slay the foul monster foe, or for more prosaic reasons, like rewarding good deeds.
The level of direct control which the Order exerts over human affairs differs from place to place; from apparent indifference and disregard in Polove, to repressive micromanagement of civil society in Lescatie (although even there, the monarchy of King Castor continued to exist alongside). Order lands are said in general to be more prosperous and culturally developed than others , while monster-friendly states tend to attract "ruffians" and aren't as hard-working . At present (and following the defeat of Lescatie), only one Order nation has actually been named: Welsple, a scholarly monarchy where Saphirette Spherica was apprenticed in her teens .
The Order's prohibition against monstergirls is not without nuance. Not all the religious nations are equally zealous, so particularly peaceful and useful monsters might even receive official toleration, like kobolds, holstaurs and Weresheep.
Extra Ecclesiam Nulla Salus
Since the Order constitutes the majority of Humankind, it may be more instructive to consider those people who aren't part of it. Monsters and Demon Realms are obviously excluded, although the Order makes use of some monster products when there is no alternative, such as sea voyages  or Magic Gem spellcraft.
Monster-friendly states are human nations which co-exist with monsters in open defiance of the Chief God's commandments, while heresies like snake cultism and the Elemental faith fester in secret within Order territories.
Organisations outside the Order which also are anti-monster do exist, the most notable being the monster-slayers of Zipangu like the Amanomiya clan. The Order seems to have no problem with other non-humans besides monsters, e.g. non-corrupted dwarves, fairies, elementals, and elves. For example, Sasha does all she can to try and bring the half-elf Primera into the Order; it is Primera's dislike of humans that makes things difficult, not the Order's dislike of Elves .
The Order; Organization / Human (Early settings info)
An organization that reveres the being known as the “Chief God” of the divinities. Its influence forms the basis of common knowledge and culture throughout most of the human world. Its doctrine preaches about the right way to live as a human being. Clean living without drowning in pleasure or other desires is regarded as virtue. For that reason, they are fiercely hostile towards the monsters which drown in pleasure and corrupt humans. They claim that “The Monsters are evil” and in many of the churches, they hide the truth about the monsters and are spreading the lie, “Monsters kill and eat people,” among the humans.
Also, that isn't the only reason why they are hostile towards the monsters. One of the reasons is also that they feel a sense of impending crisis. Since the children born between humans and monsters always end up being monsters, it could lead to the decline of Humanity.
On rare occasions, lesser divinities such as Angels appear to convey the word of God, or to join in assaults against the monsters.
From the standpoint of the monsters and those who love them The Order seems like the great evil in the world, but most of its members follow the doctrine and lead virtuous lives, such as priests, holy knights who have a sense of justice, and benevolent sisters.
Also, most of the humans revere the “Chief God”, but it is said that other religious organizations exist that revere other Gods.
The Order is the religious organization that reveres the Chief God who is purported to be the creator of the world. The Order isn't monotheistic, there are many Gods, but all of the other Gods are regarded as subordinates of the Chief God. Faiths that revere the other Gods are treated as sects of the Chief God's religion. For that reason, the majority of humans are adherents of the Chief God. The majority of nations have established the Chief God's religion as the state religion. Most of the human world is controlled by this enormous organization, and humans have values that conform with its doctrine. The doctrine of the Chief God's religion explains how to live one’s life properly as a human. Virtue lies with maintaining to be noble in character and pure of heart, never drowning in lust and other desires. Clean living is regarded as virtuous. The followers of the Chief God's religion begin every day by praying to the Chief God, and they continue to be virtuous, according to the Chief God's teachings. They lead clean and quiet lives. And because one of the teachings says to 'love thy neighbour', they treat other people who are followers of the same religion with kindness.
However, according to the Chief God's teachings, 'love thy neighbour' doesn't include monsters. They are taught that monsters have been the enemies of Humanity since the age of the former Demon Lord, they are beings who corrupt, and lead mankind to destruction. (Actually, if the children born between human men and monsters are only female monsters, then it would gradually lead to Humanity's ruin.)
For that reason, they are hostile towards monsters. The Order's knight brigades, etc. will aggressively attempt to slay monsters as soon as they spot them. They also form armies and try to invade the Demon Realm. Additionally, people called “Heroes,” who receive orders to slay the Demon Lord from The Order, are under the divine protection of the Chief God. They boast far more powerful combat abilities compared to an ordinary human, and can overwhelm monsters.
However, because of the benevolent nature of Heroes and holy knights, when they actually get in a fight with monsters, many of them hesitate to bring their sword down on a monster in the form of a woman, and in that moment of vulnerability, the monsters catch them off guard, and they end up having sex with them. No matter how strong the will of the knight or Hero, they are still men after all, and they are unable to resist sex with monsters who have bodies that are specially adapted just for pleasuring men. After having sex with them, they know devilish pleasure for the first time, and learn of the deep love that monsters have for human men, which results in them becoming prisoners of the monsters. They will probably end up choosing the path of living with monsters. Additionally, these countries that are controlled by the teachings of The Order, and have hostile policies towards monsters are called “Anti-Monster states.” Most of the “Anti-Monster states” are comparatively affluent, and boast a high cultural standard due to the teachings of the Chief God.
↑Demon Realm Traveller's Guide; Demon Realms; Earth of the Demon Realm
↑Monster Girl Encyclopedia I; God's Servants and the Structure of the World; 1-1 The Order and Anti-Monster States