For My CK2 Pagan Russian AAR I did delve a bit into how the religion began to change and evolve. Using some of the mechanics for inspiration. Most notable in the fact that 4 branches that Autonomism gets(Tribal, Syncrenistic, Spiritual and Militerist). There are elements of chinese thought in these branches but that was as Russia became tied to China through marriage alliances and trade between them and the Tang Dynasty.
All 4 branches focus on the concept of Rovinuyj or being at harmony with the world. However, naturally each of the 4 branches would come up with different concepts on how one maintains such a harmonious world.
- Kolesi - The Spiritualist Branch. This branch focused on living a simple life and honoring the gods. It would come up with a ontological dualistic cosmology which contrasted with the dualism of Russia's neighbors. The passage of the Sun and the Moon create a day is an example that is used. Temples of Chernobog and Belobog would strongly support this branch to the point where they were one in the same. Also these temples became famous as temples of black and white due to the doors having one side black and the other white but both sides had a small element of the other color somewhere in it, generally at the top to represent the sun and the moon.
- Radociti - The Tribalistic Branch. The two big focuses for this branch are living a wise life and honoring one's Family,both living and dead. This school would also coin the term Prav or Divine Law. It believed that a family must educated into ensure that wisdom is passed on from one generation to another. It also extolled the concept of the Family as a model for the nation, with the emperor as the Father of the whole empire.
- Akamirciti - The Syncrenistic Branch. Acts of violence threatens harmony and bring the world into disorder. Peace between Tribes brings harmony. its big concept is Mira or World Peace which had the concept of Vunemira and Vnitrnimira or External Peace and Internal Peace. Thus Vunemira focused on compassion and resolving conflicts between tribes;especially preventing blood feuds that were common during this time. While Vnitrnmira focused on being at peace with one's self. It would also develop a number of meditative practices(more similar to Buddhist and Taoist Meditative Practices than christian).
Sviatociti - The Militerist branch though its main focus is Justice. Balance is when a Just leader delivers justice. Its the branch that comes up with the slavic concept of a 'just war'. This branch tended to be the most hostile to Christianity than any other branch. It is from this school that many of the Russian Martial Arts would come from.
The idea I came up with is that these 4 schools of thought while they could had their differences did draw on one another's idea. For example the Radociti branch came up with the concept of Prav but the Sviatociti branch would also use the term to help explain Justice and what a Just war is. Also with the exception of the first branch of Kolesi, all of them were named after the semi-mythical founder. So Radociti for Radoslav, Akamirciti for Akamir, and Sviatociti for Sviatoslav.
This reflects the theological developments that affect the nobility and elite and played a role in shaping the empire. For commoners things were much more simple. Honor the gods, attend the animal sacrifices(and get offerings of free meat) and do what you were told to do. Sadly I stopped before I got to the part of transitioning from Feudal to Imperial government which due to the ties with China would have meant creating an Imperial Examination System that had these various branches and the other religious works as key things to know and study to pass.
Though other religious developments I included was the development of temples, which often were wooden at this era and included many elaborate painted drawings of mythological stories and events related to a particular temple. Later on as stone temples started to become developed this would lead to Mosaics and Murals for the temples of those events. As I was Autonomous that meant there really wasn't any religious hierarchy and most temples tended to be a family affair, where the son or in a few cases daughter of the previous Volkhov would take over after them. One thing I did come up with was that the Priests helped to spread the writing system that was developed and tended to be among the more educated of the classes of society.
So uhm that is how I fleshed out Slavic Paganism for my ck2 AAR. Thoughts?