He remembers all there is about Dean Winchester.
He remembers January 24th, 1979, when a little human was born and was given the name Dean Winchester. He remembers he received an order to pay close attention to this baby because, God softly whispered, one day he is going to be indispensable and one day, Castiel, you of all beings that have walked the earth would understand what that means.
He blankly smiled as the mother Mary cuddled up the wad of blanket and proudly showed it to the father, neither could take their loving eyes off of their son. Even though he didn't know what God intended for his visit, he basked in the familial joy all the same. He had been through many wars and plagues and much human indecency, he found solace in the invincible power and purity that is family.
He carefully placed his palm on the baby's forehead and in return received a wide but fleeting smile drowned out by random muscle movement characteristic of an infant's underdeveloped neural system. What a smile, he could feel the sun come out in the misty weather of January.
"Hello, Dean."
He greeted the baby for the very first time and stayed at the hospital for the rest of the day. He memorized the shade of his cryptic green eyes, and managed to get Dean to open his eyes multiple times by tickling his toes, he thrashed his stubby arms around as if Castiel had interrupted his precious nap time. He remembers his little temper. He sat contently watching over the fate-changing baby, Dean Winchester, contemplating what it all meant.
It was about dawn when he heard another angel landed quietly behind him.
"Cassy, we need you back in Heaven. Now."
He looked back and Balthazar was inches away from him, face ridden with urgency. Words of unease and whispers about Hell's plan had put Heaven in high alert, every angel was scouting out as many demon's whereabouts as possible. They had yet to find Azazel, and Castiel understood his time couldn't be wasted doting over a child. He held up a finger suggesting Balthazar to give him one more minute, he turned back to Dean and looked over the boy that was assigned to him by God, whom one day is supposed to teach him the real meaning of indispensable. He suddenly felt great sadness to leave, a looming premonition warned him their next meeting would not be pleasant. He was gripped by the wrenching feeling in his heart and couldn't gather himself to say goodbye, instead he planted a kiss on Dean's forehead and quickly fluttered away with Balthazar, leaving no trace that he has ever been here.
It would be a long while until Castiel finally meets Dean again. But he remembers everything that had happened that day, and those calming green eyes have never left the back of his mind.