Visenism

The northernmost of the monotheist faiths that mostly shared eastern parts of Imperium of Karadia between eachother. Visenism is a faith that originates in Kingdom of Visenia (from which it also took its name). It can be considered its state religion, that by extension spread to all regions under influence of visenian kings. Meaning that it is prevalent for example in Poleshya and even in Dragonbone Mountains it gained many converts among local elves.
Despite being monotheist religion it doesn't actively search for new converts, being mostly happy with being one of the Vassal Religions of Imperial Religion. There are still a lot of local previsenian cults going on, even though through the several millenias of visenian influences managed to (mostly) make them accept some sort of at least outward visenian form. With local previsenian deities and so on over time turning into a servile beings of Lady and so on.
This lack of active proselytism (willing converts are still accepted and welcomed) is mostly caused by the fact that visenianism is, ultimately, a failed polytheism. In prehistorical times its current chief deity (Lady) was a singular benevolent deity in a pantheon made mostly by warmongering maniacs. It ended when she rebeled and managed to defeat them, forever deposing them and take away their godhood. Her 'singularity' soon changing her religion into a monotheist one, while making her ascend into the Greater God.

Gods

Lady

Lady is a monotheistic Greater Goddess that remains a center of visenian religion. She is also known as Bright Lady or, simply, as a Goddess. She is pictured as a strikingly beautiful lady in a rather conservative dress. As all Gods of that level, she is mostly withdrawn, preferring to act through her multitude of servile daemons and local deities. She concerns herself mostly with making sure that the other gods of her ancient pantheon never manage to achieve their vengeance. Which she acheives mostly by slightly tipping the scale, helping her believers achieve that by themselves.
She is an omnibenevolent divinity, one that isn't unlike most other monotheisms - meaning she values free will and improvent of her believers. She also still carries many signs of her ancient self (a water-aligned divinity of motherhood and families), being especially protecting of families and with water often playing an important role in rituals of Church of The Lady.
She played an important role during creation of Imperium of Karadia. Many of the warriors that accompanied Falon the Conqueror in his march south were Visenians. With thousands of them settling as imperial nobility they left their mark on imperial gods during the period when Imperial Temple was being formed. Mercy, Imperial Goddess of mercy and forgiveness, was (according to very early imperial theology) a daughter of Bright Lady and Ember.
Goddess can be thus simply considered a very source of what can be described as purely good part of Imperial Religion. Which, beside it, deals with greys a lot.

Archdemons

Archdemons are what remains from ancient pantheon of the Lady. They are remnants of other gods that she stripped of their godhood and forced into a crossbreed between regular god and archdaemon (they generally are gods, but the religion they are a part of violently denies their status, meaning they remain somewhere in the middle). They are called Old Gods by those that still worship them.
They are led by Svarov, believed to be former chief deity. There are five main archdemons - Svarov, Piorun, Mokosz, Velevit and Mora. There are several lesser, but their lack of 'fame' mostly led to them being barely more than glorified archdaemons. The archdemons themselves are extremely strong (to the point of them never showing up in Real World in their own form) and very proficient in manipulating mortals. They permanently try to undermine the Church of the Lady.
...also causing famines, daemonic incursion, and all the other things that nasty daemons are capable of. They themselves reside on the far outskirts of Lady's Garden, forever barred entry to their own former world.

Theology

Creation Story

Visenism is, in a way, very similar to Imperial Religion. It doesn't really specify who created the world. It accepts that it might have been a completely different deity (it isn't specific in that matter), but it also could have been a Bright Lady. Lack of some well defined central scripture remains a problem in that matter - overwhelming majority of Lady's teachings are based on tradition and her rare interventions. There is a lot to be doubted in that matter.

History

The biggest problem with visenism is that its origins predate the discovery of writing by the people of Visenia. Thus most knowledge about Lady cames from oral tales that were probably really, really old when Visenians finally learned how to write. Meaning that most of them are pretty much debatable, tend to exist in at least several version in various areas and so on.
Biggest piece of story regarding the foundation of visenism is the tale of Lech Wheelwright. A legendary first king of Visenia, that led visenians in their march west which, in turn, led to them settling lands that they today inhabit. He achieved that by defeating many daemons (mostly ones subservient to the archdemons) with the help of Bright Lady. Which is believed to be a remainder of the tale of Lady's religious coup.
Ever since then the visenism remained as it was, slowly spreading but without any organized attempts of proselytism. It was severely undermined by repetitive svarovian urprises and civil wars they caused. They remain an everpresent threats, since even if Church of the Lady manages to completely extinguish their sects thriving on the outskirts of civilization, their 'gods' will simply make new cults.

Afterlife

Visenist afterlife is called Lady's Garden, or Heavenly Garden. It is pictured as a transcendentally beautiful place of eternal happiness for those that remained faithful to the Lady. It is surrounded by the so called Outskirts, a desolate wasteland which is ruled by Svarov and other archdemons and inhabited by those that forsaken the Goddess and turned to them.
There is a semi-permanent war waged theere, as archdemons are more than capable of forcing their way into the Garden. They attempt that over and over again, on the forefront of massive armies of sinners and servile daemons, forever trying to retake what was once theirs. They are, however, always repelled by the Lady, her servile daemons and the honourable Dead (mostly knights and other warriors that now spend eternity protecting their brethren).