The least powerful of all the deities are the tertiary goddes. They represent the smallest portion of the various planes, with more limitations than the other goddes due to their peculiar formation. The tertiary goddes begin as mortal souls. Upon their death--often untimely and heroic--they ascend into godhood. There are two methods of ascension.
The most common method usually applies to theocracies, or to a lesser degree monarchies. A great ruler who claims divine rights dies, beloved by their people who already believe they are at least partially a deity. Often this is accompanied by various prophesies, great public rituals, or a symbolic divine marriage (for example to a goddess of fertility or of the land) throughout their lifetime. This primes the people in their faith in their ruler, Upon their death, the soul begins the normal process
of detachment from the body.
However, a key difference is that the collective Effect of Belief
acts immediately on this soul, forcing it to retain its general nature. Many people confuse the resulting personality for that of the original mortal, but in fact it is made directly from the collective belief. The original soul forms a foundation that contains the most impactful traits and memories from their life, yet their journey differs from the average soul. The aspects of their self that match the public perception are anchored, while their private self is allowed to fall away. Over time, this tentative framework is reinforced with the national story, and they become a full representation of the needs of the people.
The people often share common beliefs about this spirit. They will protect them in times of need, offerings to them keep the nation strong. The rulers who follow the ascended one are wise to tie their own power to the beloved spirit. Over time, a nation may accumulate multiple tertiary goddes whose original memory is lost over time, retaining only that which serves the people's current needs. They become figures of myth. Their stories may or may not include their ascension. More often the stories are framed as their divine nature being true all along. Like secondary goddes, their nature is malleable over time as beliefs change.
The tertiary godde must be attached into a larger plane. Their soul will quickly reach maximum capacity, but since they have no corporeal form, they will be entirely dependent on their worshipers. Any small lull in worship might use up their reserves. They dissipate in the natural course, and the people go on praying to an entity that no longer exists. However, if they are tied into associations with one or more classic planes, they are much better able to last. Usually this takes the form of one of the primary domains, if the people did not already have a secondary godde for that plane. Or the will of people might attach them to a secondary godde-- this is similar to the second method of ascension below, but has distinct implications as far as the tertiary godde's ability to maintain their own independence.
The second method of ascension is less common, and involves a secondary godde who takes a liking to a mortal. On their death, the secondary godde anchors the soul, preventing it from dissipating through the usual channels. They are given a section of the secondary godde's part of the primary plane. This has an enormous advantage, as the tertiary godde is able to draw immediately on a larger source of power. They are less likely to disappear, as people will worship both goddes, strengthening them together. There is a disadvantage, however, as the secondary godde truly controls the plane. Ultimately, the tertiary godde will be only a facet of the secondary.
It is possible that a tertiary godde will be so popular that their worship will totally eclipse the secondary godde that sponsored them. Over time, the people reference them together, then gradually leave off the secondary godde for the more popular hero. Finally, the secondary godde is forgotten, leaving traces only in art or as a named mention in a story. It is unknown in this case if the secondary godde merely takes on the full guise of the tertiary, or if the tertiary grows enough in power to overtake the sponsor. The effect to the people is the same, as they go on worshiping their favorite godde until the next stage or end of their culture.