Disclaimer: Definitely not mine; I don't have Kripke's sheer, twisted genius.

A/N: This one was unusual and fun; most of my SPN has been Sam/Gabriel, but this came out of nowhere. And yes, I might very well do a sequel to it at some point. Enjoy!

It has been many, many ages since he saw a soul as beautiful as Mary Winchester's. He stands before her, invisible to her eyes, and simply marvels at the glory of his Father's creation. He was drawn here by his future self's presence. Time travel is not something to indulge in lightly, even for those few powerful enough for it, and he came to see what his future self found so urgent that it caused him to meddle where perhaps he should not. He did not expect Mary.

He can't resist, even though he knows he should. He knows what her destiny is; it was Writ long before she was born and it will unfold with her death. She is the Mother, her purpose to Bear the Vessels and the Martyr whose sacrifice will set her sons on the path that will end in Paradise. He knows all of that.

But for once, he doesn't care. This is temptation, and Father forgive him, he cannot resist. He finds himself watching her. He guards her as her belly grows with the son who is his rightful Vessel, he watches as that Vessel is born and Mary cradles her son to her with nothing but sheer love in her eyes.

And Michael wants her to look at him with that adoring affection she casts at her mate.

He watches, telling himself it's only to ensure that no harm befalls her until the appointed time. She is, after all, a hunter from a long line of Hunters all the way back to Samuel Colt. Even worse, she's made a Deal with Azazel and his stench lingers about her soul, not quite tainting her, but leaving its mark nevertheless. He watches her raise her son, watches her love her husband, watches and watches until the temptation is too much and he can watch no more.

It's a hot August night, and John Winchester is working late in the garage he shares with another mortal. But what matters to Michael is that he's alone tonight, so there's no one to notice when he arrives. It's hardly the first time he's possessed John, and while the mortal's conscious memories are wiped clean with a brush of Michael's Grace, his subconscious remembers—and it associates Michael with truth. So when Michael asks for John's consent, saying only that it's necessary—which isn't a lie, precisely—John says yes. Michael sweeps in carefully; the mortal isn't as perfect a fit as his infant son will be, but he's more than sufficient for a brief span of time. He puts John's soul to sleep and gives the jumble of parts a baffled look before his Grace deposits them where they belong—he doesn't want John to suffer for this night. Then he climbs into the vehicle and drives off, using his vessel's knowledge to accomplish the bewildering task. It's late enough that young Dean is asleep, tucked safely in his bed, and Mary meets him at the door, light spilling around her and a smile nearly as radiant as Michael's true form. The vessel's chest feels tight at the sight, but he dismisses it, making a mental note to ensure the vessel is in perfect health after his departure; it's the least he can do, all things considered. He ignores her soft offers of the plate of food sitting in the oven and steps in, giving into his lust and kissing her fiercely, the flesh between his legs hardening and aching as her taste bursts across his tongue.

He's never felt this before. Angels mate, yes, but it's light and Grace, not this clumsy mortal business. But he wants her so badly.

Mary is laughing quietly as she leads him up the stairs, flushed and giggling. He skims his Grace over the closed door where a toddler sleeps, sealing the room with his protection and ensuring they won't be interrupted. He lets Mary tug him into the bedroom and down onto the bed and her.

It's nothing he's ever experienced. She's soft and warm, arching under his curious hands and crying out softly into her fist to muffle her noises as he tastes her, delving into her with tongue and then fingers before he slides in. She's soft there too, wet and hot and welcoming, and the vessel knows how to move and what to do before he can even think of seeking out that knowledge. He thrusts into her over and over until she cries out, muffling the sound against his shoulder this time, and clenches on him, and then he's spilling into her, waves of heat and his vessel's seed laced with his Grace, and he doesn't want to leave, wants to stay here forever buried in this vessel and this woman.

It terrifies him, makes him realize what he's done and how many unspoken laws he's broken this night, and for a single horrible instant he thinks he hears Lucifer's laughter ringing in his ears. So as she curls into his vessel, Michael puts Mary to sleep and flees.

It's only much, much later than he'll realize he left more than he'd thought behind.

It's nine months later, as mortals reckon time, and the news has spread: the second Vessel has been born. Michael holes up in the dwelling he claims as his own and doesn't listen, ignores the mortal world until the night Mary dies. Her Deal didn't claim her soul—that wasn't what Azazal sought from her—but she doesn't come to Heaven as he'd half-expected and half-dreaded. He dares to check only once, and when he doesn't find her he shoves it all aside. And he doesn't go looking for her children.

It's years later as mortals count time that Mary Winchester's soul finally returns home. Michael doesn't hesitate, but instead carefully tucks her away in a tiny corner of Heaven that he's warded thick and deep with his own protections. Her sons are Vessels, but Mary isn't going to be a bartering chip used against them, no matter what that upstart Zachariah thinks. When John Winchester, the brimstone and sulfer of Hell still lingering about him, finally ascends, he joins his wife.

Events unfold as they must. Lucifer walks the world once again, and he awaits the consent of his rightful Vessel. Then, finally, the event that started it all, and he rushes to the past to stop Anael from her mad quest to prevent the destined battle by ending the Winchester line.

And for the first time, he realizes the full impact of his decision years ago, and in the future. Because the tall boy who is Mary's second son has threads of Michael's Grace woven into his very being.

Son of mortal woman and angelic father. Half-blood. Nephilim.

Michael's son.

He reels under the knowledge even as he does what he must, tells Dean the battle against destiny is futile, using his words to break the boy still further. But his touch is gentle as he heals Sam, returns his soul back to the not-quite-mortal frame housing it, and sends him home again. Dean follows, and Michael flees back to Heaven.

Sam is his son. But his Father's Will in this is clear: the battle must be fought, and Sam is Lucifer's Vessel as Dean is Michael's.

Sam is his son.

His Father has commanded.

Michael finds himself torn between his love and devotion for his Father, and the small, fierce surge of love that poured through him when he saw his fledgling for the first time. He finds himself watching over the boy, occasionally stepping in when the situation seems too dire for the fast-Falling young Seraph to handle. And if Zachariah is led astray a time or three, well, the Vessels are his concern more than any other angel's.

And still the war inside him rages.

He is tempted, sorely tempted, but this time he cannot waver. His Father's Will is clear; Samuel's destiny is set by Writ and Prophecy both. For the sake of the world, Sam must be Lucifer's Vessel and Michael, wearing Dean, must strike him down. As it is Written, so must it be. Michael strayed once; he does not have it in him to stray twice. But that does not mean all will be lost. He will strike down Lucifer and grieve for his brightest and dearly beloved of brothers, even now. And as Lucifer dies, he will cleanse his fledgling's soul of any and all taints, and shepherd his son to Heaven himself.

It is the perfect solution. It is the only solution.

So Michael waits patiently…and finds himself thwarted every bit as effectively as Lucifer. If it wasn't so annoying, he'd admire his son's sheer stubborn will. As it stands, he's forced to take the youngest Winchester in the eldest's stead. Adam is not the perfect Vessel Dean would have been—but he'll do. And it still isn't over. Thanks to the mortals' stubbornness, and Gabriel's trickiness, they retrieve the rings—and, finally, Sam says yes.

It's time. It's nearly over, and he is so tired. He just wants it over.

Michael appears on the ordained battlefield, faces his brother and prepares for the final battle. And then Dean Winchester arrives, that upstart Seraph has the sheer gall to temporarily banish Michael by use of Holy Fire, and by the time he manages to reassemble the Vessel and return, the Gate is open and Sam is in control. For a second he simply gapes, because even a Nephilim shouldn't have the power needed to control Lucifer, and he can see his brother raging and flailing to no avail as Sam bides his brother farewell and turns to the Gate.

Michael tries to stop him, because it has to end here and now. This is what is Written. Returning Lucifer to the Pit solves nothing; he will simply escape again and in the meantime, the war will continue to rage with humanity caught in the middle, pawns to angels and demons alike. That can't be what Sam wants. Surely, he'll see reason.

But he doesn't. He casts himself into the Pit and Michael cannot stop him. But…in the Pit, Sam will be left entirely to what shreds of mercy Lucifer still retains, and it will be little. So Michael, worn and exhausted, makes the choice—and Falls with his son, his brother.

May Father have mercy on them all.

FINIS