Random idea, I know it's not perfect and it's pretty shittily put together but what are you gonna do? I kind of like it and I don't know if anyone else has already done this so…
I think I might add another couple of chapters to this about Cas falling. I have this big headcanon about the type of man Cas would be when he falls and how his grace would go and stuff.
Oh, he's fallen!Cas in case you don't get that and he's like… reflecting or something.
Dean was surprised when Castiel, Cas, a human formed by Dean's own hands, began to write to pass the time between hunting, sleep and food. Poetry filled paper faster than Dean could find it and then Cas would scrawl on napkins or in the columns of books or scratch it into tables as they passed through.
Dean was surprised, but Cas was not. He had his inclinations, a story from a billion years before Dean was even considered in Heaven. A billion years before the close had even began to be thought about. The other side of this story- not the end but the beginning.
He had stood at the oceans edge, peering into the infinity that his Father had created for them. His grace shone softly in the dulling light, one of the first of many nights that his father would bend the heavens for. The sun had just set and Castiel, fresh in creation, reveled in being at a shoreline watching a little grey fish heave itself up onto the beach.
He shuffled closer, his elder brother bending over slightly to inspect their Father's works. The elder was not aware of his brother's purpose, nor the role that he would play in the years to come. He did not know of the Winchesters or how far heaven would fall. He simply had been told to pass the word of God through him and to him, in turn to pass to others in His worship.
"This is a sacred moment my brother," the elder angel said. The sternness that the voice usually held had disappeared in wonder, as if there was an incomprehensible beauty in the words the fish could not yet understand. "Our Father says it is His great creation to come."
Castiel was confused as to how this creature, dulled in the skin it possessed, whose complexities he could map in a single instance or in the palm of his own hand, would become such a being. The greatest creation of God. However, he accepted what would come and could become, for it was the word of God and God's word is law.
So it was with fear and love he watches the fish as it began its terrestrial life by closing the gap between the young angel and itself. Startled by the action, Castiel took a step sideways. His brother frowned for fragility of the creature.
"Don't step on that fish Castiel," he said, the sternness returning to his voice. Castiel replanted his foot away, bending down to crouch and peer like a child.
"Such a thing, does it understand it's significance?" He asked, watching the slippery skin clear slowly of the nutrient rich waters.
"Not as of yet. At this stage anything could come of it. Anything could influence it's development."
And though it was not the Lords command, He did not command against it and so Castiel whispered quietly to the fish so close to him. Ancient poems, even at this time of creation, in enochian that seeped through the skin like oxygen. Timeless poems that told of the beauty that would not be remember in years to come. This ocean, the waves that crashed furiously as the earth settled into itself. The smell of newness that the air had, unparalleled by anything following. Lines that had been put in his head not by God, but by creation itself. The fish appeared to slow its movements, stopped by the words. He weaved a cloak of passion in an infinitesimally small moment to dry God's Greatest Creation with, and planted a seed of the same passion within.
The words stopped short when he heard his brother behind him. Laughing. Cold chuckles passed through the young angel and rolled into the sea.
"It cannot hear you brother, it cannot understand you. There are big plans for this fish. They have not been finished yet, Castiel, you cannot teach poetry to something so immature." Something akin to shame pressed its lips to Castiel's neck and sent him up to the standing position.
"Of course. I don't know what I was thinking."
And so the angels returned to preach the word of the new beginning, the compulsory love of the Lords creation ringing through Heaven. Those disloyal to this were found cast into hell, including one of the archangels himself. Gods love for what his creation was to be outweighed even his love for Lucifer who was loyal only to him. Perhaps it seemed unfair but they were to follow the Word, as the Word was God and God's Word is law.
Castiel, of course, did not question the words his elder brother had given him either. He harbored the disappointment of false roots inside himself until a time so many years later in which he fell from grace, torn from him by Love fit not to God but to Humanity. Cast out of heaven for following Gods word, shamed like the archangel because he was the opposite.
So Dean shouldn't have been surprised when Castiel wrote endlessly. Or else he would not of if this past in timeless origins could just be explained. It should be expected from the being that in secret gave passion to life itself. Castiel, teacher of truth and faith, freedom and the obedience, poetry to fish.