Narrative causality is a metaphysical force that exists within most of the multiverse. It causes events to follow stories with a beginning, a middle, and an end. The laws of narrative causality vary from universe to universe, but they tend to have common elements.
Megacrossover Earth has very strong narrative causality, which probably explains why it appears in so much of Earth-Prime's fiction. It tends to favor heroes fighting against villains and otherwise normal people overcoming obstacles despite improbable odds. The most important rule of narrative causality is the "rule of drama", which states if there is potential for conflict, it will never be passed over.
Another important part of narrative causality is the hero's journey, where a person sets upon a quest that will result in them becoming a great hero.
Both the Elder Gods and the Archdevils are aware of narrative causality and take advantage of its different forms to pursue their goals. However, they try not to manipulate the stories too much since that would result in hubris leading to their downfalls.
Every species and civilization in the multiverse is believed to be involved an overall "Metaplot" that is said to have started when Eru first created sentient beings. The Metaplot is believed to involve the conflict between different opposing forces and concepts. The Elder Council-Archdevils conflict is the most prominent manifestation of the Metaplot, although the Great Old Ones and neutral entities are also said to be players. The Metaplot is said to be so strong that only a being with a Super Weight 7 can alter it.
On occasion, some beings in loosely controlled shadow worlds are able to subconsciously manipulate narrative causality, causing them to be virtually unstoppable heroes or villains. These individuals, known as Mary Sues, are considered to be dangerous by the Elder Council since their actions can have disastrous effects on their universes' plots. Highly trained agents have frequently been sent to kill Mary Sues and restore order.