Xythys (Zithis)

Xythys is the god of fire, and the sun. Primarily worshiped by the residents of Cadrin, many offerings were given in search of protection and bountiful harvests under the watchful and life-giving sun. They believed that Xythys is the highest of all deities and protector and leader of the three Divinities. They believe that they are the god who created everything, and breathed life into the land. More importantly is the idea of fire and warmth, their fires are capable of bringing warmth in the cold winter nights to protect their children, but also to burn brightly and burn away the sins of their followers.
The denizens of Cadrin often built temples in their towns and cities. There was worship of the other gods within Cadrin, but it was hardly common, and there were pockets of religious fervor that existed within the Kingdom. Most notably, the extreme worshipers of Xythys were against the marriage of King Miraberos and Queen Adelyth based on her heritage. They believe that the Frostborne go against the will of Xythys by living in the Ice Flats, and were the few to reject the large cultural shift of the century before the Shattering.
Xythys is worshiped in the other countries as well, though not as widely. The worshipers outside of Cadrin believe them to be more of a watcher, content more to observe than interfere in the mortal world. Those beliefs were more widely held pre-Shattering, before calamitous events drove many towards fanaticism in an attempt to comprehend the atrocities and horrors that were happening.
Their symbols include the image of a heart-shaped flame, mostly used by those in Cadrin. The other countries typically use the symbol of an eye within a sun. In a post-Shattering world, the imagery used is the heart-shaped flame, carried over by refugees from Cadrin that settled in Ezeth. While their temples and houses of worship are fewer than those of Perdita, there are still active worshipers including refugees that still live and their descendants, those that were converted by the refugees, and the more fanatical denominations, however rare those may be.
The story behind how Xythys came to power and created the world changes with who answers and their denomination. However, the most common origin story believe they were a powerful angel who came from another plane and upon finding the beauty of this land, breathed life and magic into it. In granting so much power into this land, it granted them the power of a god, and they've watched over this land ever since.