Sam had gone off on a hunt on his own when Dean found himself stuck in the future by Zachariah. In five years, the world had gone to hell in a handbasket. People were running around infested with the Croatoan virus, and he was the leader of a small camp of survivors. To top this interesting little crapfest off, Castiel was a drug addict. Illegal or over the counter, it didn't matter to the former angel who tried to get over the pain of being sundered from his brothers by hopping himself up on booze and pills and losing himself in orgies. It clearly didn't work however.
He'd apparently arrived at camp in time for the final showdown between his future self and Lucifer. Not being something he wanted to miss out on, he invited himself along for the ride with a pill popping Castiel who was staring at him as if he'd never seen him before. The showdown went pretty much as expected, everyone died horrifically and Dean found himself alone with Lucifer who was hainging out in Sam's body. Sam who looked at him with that cold fake pity as he offered to take the conversation to someplace more comfortable "Like home perhaps..."
With a snap of his fingers that stirred something in Dean's memory, he found himself and Lucifer who was wearing his brother standing outside the mouldering wreck that he'd once called home during the happiest period of his life. Deciding that he didn't want to play Lucifer's sick game he ran off towards the park he'd barely remembered and his favorite tree, the Miracle Beech that he'd tried to climb any number of times and had been grabbed off of by his parents. That tree had been a comfort to him when he was small, and had drawn him to it every time he'd visited the park.
When he reached the derelict park, his tree wasn't there, and there was no sign that it had ever been there.
"What are you looking for?" Lucifer asked, coming up close behind him as Castiel was wont to do.
"My tree." he replied, as he kicked the dirt in the spot he vaguely remembered his tree being in.
Lucifer studied him for a moment before backing away in shock and gaping at him like a landed fish.
"You'll find your tree in your own reality." Lucifer finally said after he collected himself, looking at him oddly as if trying to figure out what he was, and why he was.
"My own reality?" he asked. He'd been reasonably certain that it had been his reality, just five years on, but he wouldn't put it past Zachariah to find a worst case scenario just to twist his arm and make him dance to his and Michael's tune.
"That little prick Zachariah dumped you in an alternate universe rather than in the future." Lucifer finally said. "Apparently something must've gone wrong or right as the case may be back home, or he wouldn't have brought you here."
"For what it's worth, I've missed you brother, and am sorry I had to kill you." Lucifer said as he reached out to Dean, every line of his face betraying a longing and a deep and unending sadness. "Every day since then, I've wished that I hadn't done so."
Dean frowned at this. He wasn't Lucifer's brother, and Lucifer had just killed him less than an hour earlier. It was at that point, an instant before Lucifer had touched him, that he'd vanished from Lucifer's side.
"Are you ready to say yes?" Zachariah asked when Dean realized that he was back in his motel room.
"Fuck no!" he yelled.
Zachariah lunged to attack, and Castiel rescued him at the last second, bringing him by the side of the road where he'd been waiting since he'd called him when he'd been trying to sleep.
"Thanks Cas, You mind dropping me off by the car, there's something I need to go and look at." Dean said when he found himself beside the road that Cas had been standing next to for hours.
A while later, he was parking his Impala next to a park he used to play in as a small child. His tree was there where he'd left it when he was four. The sunlight filtered through the leaves beautifully as he approached it, putting his hand against the trunk, greeting it like the old friend it was. In the second before he got his Grace back, he found himself thinking that he should've known, especially after that whole Anna debacle.
The Archangel Michael leaned against a beautiful Beech tree in a small park in Lawrence Kansas, finding that he didn't quite want the world to end, that he didn't want to lose his Sammy, and that he couldn't bring himself to kill the brother who'd had a look of unending sadness in his eyes as he mourned his loss in that other universe. He would fight him because that was what he was destined to do, but a part of him who still loved his brother even after all he had done found itself saying "Not quite yet..."
Perhaps, if nobody knew he was here, things wouldn't move forward...
With half of an insane plan running through his mind, Michael sent a silent apology to his father who he wasn't quite disobeying since he was merely delaying the carrying out of his fathers orders, hid his Grace, and tamped down everything within him that wasn't Dean Winchester, in hopes that nobody would realize. If someone messed with what was his when Sammy or Lucifer wasn't around however, they would find themselves getting an almighty surprise.
Leaving the park, Dean called his brother to tell him that he was alright, and headed to the nearest diner. He wanted pie.