Lay Your Weary Head To Rest
Michael never Falls.
It's an important distinction, they think. They never Fall, not like Lucifer. That does not mean the Cage was kind to them. The Cage is not a kind place. And Michael... Michael was not kind either.
They are an archangel, God's true might given form; power and divinity and wrath. When Lucifer's True Vessel drags them down into the Cage, they waste no time in tearing into Lucifer. The pair of them shred each others' vessels to little more than atoms then rip at wings, limbs, and grace. They scream at each other in High Enochian, uncaring of how the ancient, primordial syllables reduce the scattered, broken vessels to the jagged edges of insanity. Michael gives no thought to how their burning grace spills across the Cage, setting fire to the souls of the two unfortunate humans trapped with them and their sibling and razing them to near nothing. But nothing can die in the Cage (they could reduce those battered souls to nothing, could crush them to non-existence, and they would still heal. Slowly, yes, but they would survive).
After nearly a hundred years of fighting Lucifer, of tearing their sibling apart and being torn apart in turn, a hundred years of heavenly wrath on an unprecedented scale that would have reduced the Earth to a charred husk and destroyed every single lifeform on it, their tempers finally run dry. Michael loses their will to fight, instead retreating to a corner of the Cage and wrapping ragged wings around themselves to drown out the sounds of Hell.
Lucifer, however... Lucifer doesn't burn hot the way Michael does. The blind rage is gone (has probably been gone for decades) and instead a poisonous, freezing hatred has taken its place. With Michael retreating into themselves, Lucifer turns that hatred onto the humans trapped with them.
Michael is so lost in their grief it takes time for them to realise what's happening. Adam Milligan suffers horribly, but compared to Samuel Winchester... compared to Lucifer's True Vessel, Michael's vessel is exceedingly fortunate. Samuel Winchester's soul has been reduced to a horribly mutilated thing, tortured to the brink of unbecoming. Michael has been around since before the Universe was created and they have never seen a soul look like that before. Ever.
Wrath overtakes them and they viciously attack a surprised Lucifer until their brother has to go huddle in a corner to recuperate. Michael cradles the souls of Adam Milligan and Samuel Winchester to them and tries to soothe the souls with grace only to watch in horror as they both cringe away from the touch of it. Michael realises for the first time how the fighting of the first- and second-born archangels must have hurt the humans, sees the scars on the souls left there by their own grace and is sickened by it.
They free Adam Milligan. Send him back to the heaven the boy should never have been pulled out of. It's simple enough to do.
Samuel Winchester... is not so simple. Lucifer's grace is twisted into the human's shredded soul, slithering and binding, vicious hooks keeping him trapped down in the Cage. Michael is not a healer and removing the grace takes time. Fortunately for Samuel, Michael has nothing but time.
They cradle the quivering, tortured soul in their wings, sing to the broken, broken human who managed to derail a plan millennia in the making while all of Heaven and Hell opposed him. And Michael cannot help but admire the stubborn little creature for it.
It takes years for the trust to build between them, for Samuel to stop cringing away and to start quietly, tentatively ‘speaking’ up. He tells Michael about the Earth they never knew, not really. They have been far too cut off from the pretty blue and green planet and its occupants for far too long, but through Samuel's words they learn.
They tell Samuel stories in return. Tell of watching Creation taking place before their many eyes, of helping raise Heylel, Raphael, and Gabriel. Of the story behind Amara, the Darkness to God's Light, the Destruction to His Creation, and how defeating Her had come at a price none of them had ever dreamed they'd paying; a Mark that had twisted their beloved Heylel into the broken and monstrous being now known as Lucifer.
And then... then Lucifer tears Michael in half and they spend the next few years pulling themselves back together. Barely half a decade has passed before they manage to track Lucifer and Samuel down but the damage has been done. Nearly half a century of healing has been undone in about a tenth of that time and Michael's grace flares burning-bright-boiling in their fury. That turns out to be a mistake and Samuel pays dearly for it; Lucifer is forced to retreat but Samuel is razed to scattered atoms in the process.
The combination of Michael's fiery-furious-fierce grace and Lucifer's torture is too much. It's not the first time Samuel's mind snaps and a very resigned part of Michael already realises it won't be the last time either. Samuel remembers nothing of Michael but the pain of their grace burning him and even when they've healed his shattered mind and built the trust back up between them again, Samuel remembers nothing of their time together before but vague impressions of trust and kindness (and something that feels a lot like the love their siblings once held for them before Michael retreated to solitude and it was replaced by a distant worship).
Samuel is just as enthralled by Michael's stories the second time as he was the first, though, and that is a consolation.
Michael is ready for Lucifer next time and the time after, and nearly seventy years pass before Lucifer gets his hands on Samuel again. It becomes a constant battle between them that stretches over a millennium, the fight for Samuel Winchester's soul. The longest Michael manages to keep Samuel away from Lucifer is one hundred and twenty-nine years. The longest Lucifer manages to keep Sam from them is one hundred and thirteen years.
Every time Michael gets Samuel back, he is broken again. Human minds are too fragile to cope with the Cage and Michael thinks the insanity is the only way Samuel's soul can even try to cope with how he suffers at Lucifer's hands.
Michael is... not coping well either, no matter how they try to hide it from Samuel. The Cage is a terrible place, cut off from the choir of their brethren, and Lucifer is cold and cruel. He cannot torture Michael like he can torture Samuel, but he can still make them suffer. In their last fight, when he managed to get the upper hand, he held Michael down and used his icy grace to freeze Michael's wings and then shatter them. It was an agony they could barely comprehend, a disgusting, horrifying violation that left them trembling on the floor of the Cage for nearly a decade until they were fixed.
Samuel becomes the one thing tying Michael to sanity. Samuel needs Michael and Michael desperately needs to be needed.
And then, during one of the times Lucifer has possession of Samuel, a wonderful (terrible) thing happens; Samuel is rescued, taken from the Cage by Death itself. Michael is delighted, of course, but they are also terrified. They have no more purpose. They have nothing stretched out before them but an eternity in Hell.
Lucifer is furious, of course, and they both take their emotions out on each other for the next few years, like they had in the first century in the Cage. But Michael doesn't have that same burning wrath in them that they did then and far too many times Lucifer manages to gain the upper hand.
With Samuel gone, Lucifer seems to have decided that Michael can take the human's place. It doesn't work, not quite– unlike with Samuel and Lucifer, between the two archangels the playing field is too equal; less helpless kitten against a starving hellhound and more unstoppable force meets immovable object, both of them Heaven's most terrifying weapons, capable of destroying entire planets. Lucifer has to fight every second to hold Michael down, to torture them, and it's a battle he can't fight indefinitely.
Michael could hurt him back, it would slow Lucifer down and force him to retreat, but they are so sick of pain and suffering and torment. The most they usually manage is to burn Lucifer's limbs with their grace then retreat while Lucifer is restored by the Cage, curling their wings around themselves and waiting for Lucifer to attack once more.
It's an endless, terrible cycle that chips away at Michael until they feel as broken as Samuel was and yet there is no one there to help them.
Time already has little meaning inside the Cage but by this point it has ceased to mean anything to Michael at all. Pain, loneliness, grief, hurt, madness; it consumes Michael, leaves them a hollowed out shell. They stop fighting back and, ironically enough, that seems to be what it takes, in the end, to get Lucifer to leave them alone. The second-born archangel has no interest in the unresponsive husk of his eldest sibling.
Michael doesn't know how long they have been down there, for how many millennia they have suffered, when warm Light scoops them up, gentle wings cradling them close.
"Oh my child," murmurs a Voice that they could never mistaken. "Oh my precious Michael, what have I done to you?"
Michael buries themself into the Grace of God and weeps, finally shattering to pieces and letting their Father hold them together as they once held Samuel. And, with the same painstaking patience and effort He took to Create them, God pieces Michael back together.
Michael is still a little bit broken, just like how they could never quite fully restore Samuel's tattered, torn, tortured soul to its former state of glory, but Michael doesn't think they even know how to be whole anymore.
Finally, finally, God hugs Michael to Him, His hundreds of wings wrapped lovingly around them, and Michael speaks for the first time. "I want to sleep." They say plaintively. They have never slept before in their long, long life, but Samuel had always spoken highly of it and all they want to do right now is rest. Their Father understands and kisses their forehead, whispering,
"Be at peace, my child."
And Michael closes their thousands of eyes.
Back down on Earth, in the maternity wing of a hospital, a baby is born. This baby doesn't come out into the world screaming and crying, however; rather, they are born restful with their eyes closed and a peaceful expression on their face.