Keyblade Lore
In days long passed, before the Keyblade War, and when the worlds were still one, the ancient Keyblade warriors had developed their own unique culture, traditions, and even a religion. They were a people, who conquered lands and built great cities and established mighty dynasties that lasted for thousands of years.
Religion
The Keyblade warriors believed in two deities. The first was the God Bhunivelze' and the second was the Goddess Etro. Bhunivelze' was believed to be the God of Light and Creation, and was called the "Steward of Arda," Arda meaning "world," and watched over all living things. Etro was the Goddess of Death and Chaos, and was called the "Stewardess of the Void," or the afterlife, and shepherded the souls of the dead. Each deity had their own divine realm in which they reigned, Bhunivelze' lived in Valinor, the seat of Light, whereas Etro resided in Valhalla, the seat of Chaos. It was also believed that each God had their own source of power beyond that of mortal prayers. Bhunivelzes' power was the Light, and Etro's was Chaos. While not inherently evil, Chaos was believed to be a very destructive entity, and often associated with Darkness.
From what has been researched thus far, the ancient Keyblade warriors were a very devout people; however, while both gods were considered important, Etro was little worshipped because of what she represented, whereas Bhunivelze' was worshipped by most on a daily basis. Etro was worshipped by most only when she had to be, such as during funerals, or on holidays that may have been dedicated to her. She was not viewed as evil or cruel, unlike most early religions with gods of the afterlife, but was believed to have a deep love for mankind, and watched over their souls in Valhalla with care. Bhunivelze' was also believed to be loving and benevolent, however capricious. If one neglected to worship him for too long, then it was believed that he would send you very bad luck as punishment. Only by repentance could one hope to return to Bhunivelzes' good graces, either by heartfelt prayer, fasting, doing good deeds in his name, or going on a pilgrimage to a holy place dedicated to him. Etro was seldom miffed; she was considered far more patient, however, less forgiving. Disregarding to worship her at least when it was required was believed to be a death wish. She would curse those who cross her, and their only hope of salvation was to go on a pilgrimage to a holy site dedicated to her, give offerings and pray for forgiveness. A saying or proverb has been recovered alluding to this, "She is the Master of Death, and She can give it freely." There are no records recovered of anyone ever forgetting to worship Etro when required thus far.
Each god had symbols that the Keyblade warriors associated with them, most notably the Sun and Moon. The Sun was believed to be a piece of the Light of Valinor that Bhunivelze' had gifted the world so it could grow and thrive. Bhunivelze' had tied golden ropes to it, and then to the reigns of silver griffons, where they fly the Sun over the land every day. The Sun is what keeps the Chaos at by, and at night, the Moon shields the world from it. According to ancient Keyblade mythology, the moon was the child of Bhunivelze' and Etro. When the gods were creating the universe they realized that they needed a way to protect humanity from chaos, who would be ill-affected by it, when the Sun went down. They decided to make love, afterwards Etro labored for seven days, and then a child was born as an egg. There is no specific name for this third deity; it was simply called the "Moon-child." Etro and Bhunivelze' told the Moon-child to never hatch, or the world would be swallowed by chaos when night came. The Moon-child was sad that it would never hatch, but listened to its parents, and took comfort in the great role it was playing for the sake of humanity. The Moon was normally associated with Etro for reasons unknown, perhaps simply because she is the Moon-child's mother. The stars in the night sky were believed to be holes the chaos where the Light of Valinor could shine through.