He didn't have to. Of the few things angels can't do well, lying makes the top of that list. Lying to himself was no exception. Castiel knew he didn't have to do it. It was a primal urge, he thought, a very, scarily human, need to leave his mark upon otherwise perfect skin. When he'd been charged with this sacred duty, with rescuing the righteous man from the depths of hell, the angel had done his utmost to squash down the simmering bubbles of pride that threatened deep within. His most beautiful brother had taught them all that pride was of no use to an Angel of the Lord.
So he'd cleared his mind and heart with endless meditation and prayer in the time before he was to complete his holy task, leaving only a single point of focus within him: Dean Winchester must be raised from the depths of Hell.
With his trusted garrison fighting around him and guarding his descent into the pit, Castiel found the object of his charge in one of the vilest sections of Hades, a rack of torture meant to break the purest of souls down into the most vile of demon torturers. He was beyond prepared to pry the soul of the righteous man from the web of chains that held him there. What he was not prepared for was the sight of the man who was to save them all as he plied acts of torment upon other souls, inflicting such pain upon the poor creatures that had once been human that Castiel nearly wavered in his pursuit.
But the closer he got to the one entrusted to his safekeeping, the more clearly Dean Winchester's soul could be seen. Through the screaming of the anguished and the agony of the brutalized on the rack, Castiel saw the most strikingly beautiful human soul he'd ever been privileged to lay eyes upon in all his millennia of human observation. He nearly halted again, but so focused was he that he carried on toward this wayward son until he reached him, gripped the soul tight, and fought his way out of perdition with Dean's soul cradled as though it were an innocent, fragile child.
Once they were safely back on the earth, the seraph began to remake the human around its soul, atom by atom, molecule by molecule, using the tattered essence as a pattern. As he painstakingly crafted Dean back into essentially the man he once was, he felt many things, none of which he'd ever felt before. He had no names for these emotions but they were so intense at times that Castiel had to pause in his work in order to regain his center.
When at last his work was complete and Dean Winchester was whole once more, Castiel looked upon him with an unknown aching burn glowing deep within him. A compulsion for which he had no comparison overtook him. The angel knew what need was, this yearning. Castiel wanted. He knew exactly where the path that started with wanting ended; Lucifer surely showed them the fruits of desiring what was not yours to have.
His brother's lesson made but a fleeting appearance through his mind as he cradled Dean's head in his lap and lowered his hand to brush his fingertips across the man's forehead, down his cheek, neck, before reaching the curve of his shoulder. Castiel rested his hand upon the arm he'd remade just as a wave of possessiveness rose up within him. Before he could force the rebellious thought down, one word fell from his lips…"Mine." His grace shot out of the hand on Dean's arm for a fraction of a second before he realized what he had done and yanked his arm back quickly as though it were he that had been burned. Instead, the arm that was perfect only a moment ago now wore a permanent brand in the shape of an angel's handprint.
"Father, forgive me," Castiel begged. As hurriedly as possible he completed the work he was given to do and dared one more look upon the face that would one day cause him to fall from Heaven. With a heaviness and regret he'd never known in all his millennia, Castiel placed Dean in the earth gently and returned to his brothers and sisters.
A/N: This is my first Supernatural fic. I'm sure it's been done lots of times before but I've been mainstreaming and this was a splinter I had to get out. Please review and thanks for reading!