It was beautiful. Really, it was. Thousands of them, all his brothers and sisters, streaking down and across the sky like the fabled shooting stars that humans wished upon. Bright and pure; they're angels after all. He shouldn't be surprised that even falling they are so much more graceful than he ever was.
But then he sees it. It's not light the angels are surrounded in as they fall—it's fire. Shining white fire that engulfs their wings in halos of death as they are ripped, burned from their backs and their grace is stripped. His family, his fellow soldiers hurtling into the ground like Lucifer once was. He watches helplessly from the ground, his grace with Metatron, unable to catch them as they plummet and fall.
An angel should never have to experience this, he thinks as he watches one angel plunge deep into the inky black river not far from him, and certainly not all of them.
It dawns on him then, that having thousands of fallen angels wandering the fragile earth is similar to giving it a death sentence. Hundreds of times worse than the demons and monsters that already ravage the land. They should have stayed locked in Heaven, and they need to go back now before they have hundreds of new Lucifers walking the earth and even more angel turned demon to hunt.
Castiel needs Sam and Dean's help. If they were still willing to give it, that is. After all, without his "angel mojo" he was just a baby in a trench coat and he had already betrayed and let them down so many times. Someone will only trust you for so long before they give up on you.
That's when he hears it, a yelled call of "Cas!" that could only have been Dean. And for a moment, he thinks he still has a little sliver of grace, that he can still hear Dean's prayers to him. But then he sees the faint outline of the church steeple illuminated by the falling angels, and he knows it's only because he's not that far away from Dean that he can hear him.
He sighs, eyes leaving his falling brothers in the sky to turn to his family on earth, and Cas begins to walk. Navigating through the brush was hard enough the few times he had to as an angel. But with his new lungs (that have never needed air before) working overdrive to keep him from passing out and an unsteady drumming rhythm in his chest (that is way too loud in his ears), he only manages to get halfway before he is too tired—too human.
So he shouts for Dean, calls his name like he has called for him in his prayers. Cas is unsure if he will come, Sam is presumably finishing the third trial as of right now, and he knows that Dean will want (need) to look after his baby brother.
Except he can hear the thudding footsteps of Dean through that drumming in his head. His vision is spinning; all he can see is his falling brothers, not as numerous now though, the last of them just breaking the cloud barrier of earth. Cas stumbles, grabbing onto the first thing he can find. He thinks it's a tree at first, but it's entirely too warm and soft, with firm arms that wrap around him and keep him standing.
He can hear Dean shouting, screaming his name to the high heavens (well, not so high anymore), can feel his strong arms shaking him, trying to make him wake up, but everything is just a big blur, nothing clear anymore.
Suddenly he feels something incredibly soft yet insistent against his lips, and he can breathe again. He gasps, blue eyes flying wide as the cool night air rushes in and out of his lungs and his vision clears.
"Cas! Cas, come one, man, breathe!" Dean's voice is crisp and oh so comforting to him as he stares up into forest green eyes. His chest heaves in effort to take in air as Dean holds him up, keeping him from falling even more.
"Dean" he exhales, hands curling up into his familiar jacket and holding on for dear life.
"That's it, Cas. Breathe." Dean's arms and firmly wrapped around him now, grabbing his trench coat just as much as he is holding onto Dean.
He can't handle it anymore—the stress, the responsibility, the humanity. He breaks into sobs, face burying to the crook of Dean's neck, tears staining his jacket and various shirts underneath. And Dean just lets him, rocking him back and forth, comforting him like he has done to Sam so many times before this.
If feels like eternity to Cas, but he eventually stops crying like a child. He can hear Dean's murmurs of "It's okay, everything will be okay. We'll fix this, Cas, we will," now that the drumming has faded somewhat, and he knows that Dean is right.
He looks up, eyes still shining with tears, but considerably calmer. Dean gives him a sad smile and they begin to walk back, to Sam, he assumes, with Dean's whispered "Remember to breathe, stupid," ringing in the background of his mind
He realizes that everything will be okay. He's with his family and they'll fix this. They always do.