One of the issues we sometimes face as a writer, especially when creating an AU for a fanfiction, or doing an original fiction, is the need to build up a mythology for the world. Whether you’re building up a fantasy world, or developing a sci-fi death cult, sometimes you just need to round out your world with religion.
Before discussing various tips for this, I think it’s important to discuss whether you should try to build a religion. Frequently, you can make use of something that already exists. We already have a rich set of religions in the world. Greek/Roman mythology, Christianity, Judaism, Islam, Buddhism, Shintoism, Hinduism, Norse mythology, etc, etc, etc. If something that already exists will work for you, then don’t reinvent the wheel. You can change names to protect the innocent, if need be.
The role of religion
One of your first concerns will need to be the role of religion in your world. For many cultures in our world, religion provides color, dictates some customs, and determines holidays. Judaism and Christianity gave us the five day work week. Hinduism affects beef consumption in India. However, the reality is you can make a lot of tweaks to the religious practices of many people in our world, or eliminate them altogether, with minimal impact.
In a case like this, religion is more about color. Many werewolf romances feature prayers to the Moon Goddess. Normally, nothing really happens as a result. They could be praying to God just as easily and nothing would change. We know wolves are associated with the moon, so this is a simple swap for color.
Another option is that the religion strongly affects the behavior of its followers. Radical Islam is an example of this. Catholic nuns and monks are another. Religion can inspire its followers to great acts of violence, charity, compassion, or hatred. In cases like this, a society’s laws, standards of behavior, etc can all be dictated by religion. In this case, an outside observer won’t notice a direct influence by the god(s) of the religion, but it dictates the culture.
Next, there can be a supernatural influence. Priests of death may be able to kill with a touch. The Moon Goddess may bless certain werewolves with extra powers. Sailors may travel with priests of Neptune to ensure safe travel and favorable winds. In this case, the gods don’t make an appearance, but their existence is very hard to deny. Sure, these might be examples of various psychic powers, but it is more likely they are just what they appear to be: manifestations of the favor of the gods.
Finally, the gods may walk among us. Ares may stride about the great battlefields of World War II. Zeus may rain lightning down on those who dared to build a spacecraft. When gods are present in the world in a tangible way, it becomes a question of how often they interact, and to what purpose.
Religion in your world
So, with the above in mind, you have to think about how religion fits into your world. Knowing your genre is not enough. A werewolf romance could have vague references to the Moon Goddess, blessings of the Moon Goddess, or her brothers Apollo and Ares may be the head werewolves in the world (yes, I’ve run into this).
You absolutely must decide how big an interaction with gods you will have. If there will be direct contact or blessings, you are going to have to make sure you know exactly who they are, relative power, personalities, interactions with each other, interactions with followers, etc, etc, etc. You have a LOT of work to do. If you’re hijacking an existing mythology, it turns into research instead of creative work, but still a lot of work.
On the other hand, if all you’re doing is justifying some cultural quirks, you may only need a couple paragraphs of explanation, with regular references to the teachings of the Buddha or the Prophet. For this, you may only need a few key guidelines, and perhaps some typical quotes that “everyone” says.
Also, regardless, you’ll need to consider what various levels of devotion to a god/religion look like. Many Christians show up at church for a couple hours every Sunday, and do little else. Some, however, commit their lives to traveling the world helping the poor. A goddess of love may have a temple that sponsors orgies. A god of war may demand adherents spend all their time preparing their minds and bodies for battle.
Balance of power
This is where things can get interesting. Consider the history of Christianity. Being a Christian has, at various points in time, made you a criminal, been mandatory, been a sign of subjugation, or been a sign of esteem. Being a priest has been just powerful, at times, as being a king. At other times, being a priest has been nearly guaranteed prison time.
You will need to determine the role your religion takes, and how high-ranking members fit into society. A king may get his authority from the pope, or the pope may be granted his authority by a king. Priests may be the judges, interpreting laws handed down by their god, or they may be in hiding while barely holding their followers together.
In the end, religion and government may be the same thing, in a power struggle, or indifferent towards each other. You have to know how they fit together. It makes the difference between whether your characters are outlaws or power-brokers.
A word of caution
Religion can be a very touchy subject for people. As a Christian, I often avoid religion entirely when writing. Depending on who your writer is, most any decision you make related to religion can upset most any reader. If you discuss Christianity in an unflattering way, you are likely to offend Christian readers, while pleasing various others. If you make up a religion, you may offend readers who are strong adherents of most every religion.
As a result, you need to think about how your readers will react to your story’s religion(s)/mythology. Fantasy worlds, or worlds in other cultures, are usually safe to do what you want. As you get closer to your own culture, you will want to be sensitive to how your readers may react.