A/N: Thank you so so so much to ImpalaLove and toridw317 for reviewing the last chapter(s)! You guys are the best! I'm sure I'll have more to say about the finale, but for now this is all I've got. This is really mostly an internal monolog from Dean's POV.

Spoilers: Season 10 finale

Superior, Nebraska

May, 2015

"Sammy, close your eyes."

For one brief, sickening moment, Dean thinks he might actually do this.

But only for a moment.

He could never. He could never.

The bloodlust is one thing, but this… He loathes himself for even having the ability to fool them. Is this what he's become? Is this how much of a monster he really is? Dean feels sick to his stomach, feels like he's choking on air. His lungs fill up and deflate. Being alive feels like drowning.

Because Sam believes it, Death believes it. Sam believes it – believes that it's right? Believes that he should? That he would?

His younger brother lays down photos of their family at his feet, fanning them out like tarot cards. He's divining the end (for both of them), divining redemption (for him), and Dean stifles the need to puke. Nothing has ever felt more unnatural, more wrong, than this – nothing.

He can barely hear what he's saying. He's blocking it out. He doesn't want to, doesn't want to hear it, because these are what Sam thinks his last words to him are. This is Sam, on his deathbed. This is the last thing he would ever say, and that's something Dean never wants to hear. He's talking about love and good on his knees in front of his would-be executioner brother. His voice is too optimistic, his eyes are too earnest. Dean can't allow it to register. He just can't. Why is that whenever he thinks he's been through everything – endured the worst of it – life hooks him through the shoulder and puts him through the ringer one more time?

His voice is a start to his own ears: "Forgive me." For everything.

Sam obeys. His eyes flutter closed, tear-sodden lashes wetting his cheekbones. He imagines his brother might revert back to some recognizable version of himself, imagines he might shoot him a cheeky wink, imagines his lips might curl into a smirk. He imagines his cocky, ingenious brother maybe-just-maybe has found a way out of this Catch-22. His imagination runs wild.

Dean doesn't wink. Not this time.

Sam tells himself: of all the lines they've ever drawn and redrawn, this was the one they had faith they would never cross. Because then it would have all been for nothing, wouldn't it? All the lives lost, all the scars hewn into their souls? All the bad they've ever done, they've done to avoid this.

Dean wonders: is this who they really are, when it all comes down to it? Cain and Abel? Michael and Lucifer? Angel and demon? If it is, fine. So be it. After everything, he refuses to believe that anything is truly predestined; he will continue to fight against their inverted polarity, because that's the only thing left worth fighting for anymore.

Sam is different. All of a sudden, it dawns on him. Sam, for all his bitching and moaning, for all his teenage protestations and rebellions, trusts him blindly. He thought the older-younger brother dynamic had faded in the past years, but maybe it's not something that can fade – maybe it will be part of them forever. He always felt it, but this is the first indication in a while that Sam still feels it too. He would let him do this.

Sam's head is raised. Tears are leaking from the corners of his eyes, zigzagging into his temples. Dean can't remember the last time his brother looked so young.

A shutter-roll of memories passes through his brain: Sammy ages zero to thirty-two. He's watched his whole life. He's watched every moment of it, give or take a few months. He changed his diapers, he comforted him when Jess died, he sold his soul to bring him back from the dead. Even with the Mark – even as a demon – how could he? How could he ever? How could he destroy something he spent his whole life trying to nurture? That's a particular type of cruelty, one that's usually reserved for gods.

He's not Sam's father, true enough, but he's had a heavy hand in shaping the man he is now. With a scythe raised over his little brother's neck, he feels less like Cain with Abel, and more like Abraham with Isaac – he's just waiting for divine intervention, waiting for someone to stop him.

Why isn't anyone stopping him?

It's nauseating. No wonder this unleashed such evil thousands of years ago – it's perverse, it's unearthly. How could such pure, dogged devotion be so utterly corrupted?

To him, Sam is sacred. Sam is the most sacred thing in the world, far more sacred than the 'greater good.' And nothing will ever change that.

Dean levers the blade into Death's gut, knowing, as he always has, that whatever consequences he has unleashed are the lesser of two evils. He could weather the apocalypse better than the Sam's death at his hands.

His gaunt, statuesque figure withers before their very eyes. The scythe, once rooted in solid flesh, suddenly becomes free and top-heavy as he crumbles around it, into nothingness.

All the while the room is pulsing: What have you done? What have you done?

Sam looks astounded, confused, relieved, and horrified all at once. Dean feels a hot-cold tingle of panic and relief rush through his bloodstream with each beat of his heart. He helps him to his feet.

"There… There are just some lines, Sammy," he explains weakly. "Even now, there are just some things I can't do." He sounds almost glad, glad that he's finally found his limit. He genuinely couldn't have done it. Genuinely. It's easy to kill faceless people, but even the Mark distinguishes between Sam and everyone else.

A more unsavory thought creeps into his mind: maybe it's self-preservation. Maybe the Mark knows that if Sam dies, Dean dies too.

He tries not to question it.

What he does remember is that, long ago, John Winchester predicted they might end up here – that Dean be forced to kill Sam. And after all that's happened between now and then, he still couldn't do it. That's a consolation. That means he's not so far from who he used to be.

That means maybe he can find his way back.

A/N: This scene reminded me a bit of the scene in Season 5 when Dean kills Zachariah, which is why I included the winking part. I don't know how familiar you guys are with the Bible, but I don't want to be presumptuous one way or the other, so the reference to Isaac and Abraham is a story from Genesis, in case that didn't make sense. SparkNotes version: God tests Abraham's faith by asking him to sacrifice his son, Isaac, but just before he goes through with it an angel stops him (somewhere, the nuns from my Catholic school days are weeping at this oversimplification, but oh well). So yeah. Tried to end more positively with this one haha. Thanks for reading!