The Obeisance of Memory by rockpaperscissor. Rated PG-13, Gen, 139k. Summary: AU of season 4. "Look, I've got no idea who your brother is, but uh, I think I might be him. Just, y'know, alive."
fanfiction.net/s/4822628
my thoughts: Also in my amnesia reclist , disclaimer: canon divergence AUs that still continue along the same plot points and timeline as canon aren't super my thing, but I ripped through this story to see what would happen. Fantastic premise!

Unchangeable by HunterPeverell (AO3). Rated PG-13, Gen, 80k. Summary: Something happened to Sam. Something magical. When he woke up the day after Dean became a demon, it was to the year 2008 . . . the day Dean got out of Hell. How will Sam's attempts to fix this time work out? Who sent him? And how can this help Sam with his own demonic brother in their time?
ao3.org/series/124797
my thoughts: Also in my time travel reclist , this is a canon divergence that still continues along the same general canon plot points and timeline and I loved demon!dean in this one. The Obeisance of Memory by rockpaperscissor (above) does a similar canon-divergent thing (only with Dean coming back with amnesia not as a demon). This fic 's featured in my demon!bro reclist too

Aecoris' Demon Dean Series (AO3). Rated PG-13, Gen, 527k words. Summary: AU to season 4. DemonDean. Dean clawed his way out of Hell as a demon intent on stopping the apocalypse and the plans for his brother. Sam refuses to believe that this creature is Dean. They'll have to trust each other and work together in order to stop the end of the world.
ao3.org/series/37816
my thoughts: also in my demon!bro reclist , I distinctly remember the beginning of this story because it hooked me so quickly: Dean came back from hell having learned the seasons 4+5 grand plans that he didn 't in canon and so his goals (as the incorrigible demon that Dean would of course be) are to thwart both heaven and hell before it 's too late. It 's riveting, and iirc the slow burn development of Sam+Dean 's brotherhood is the lovely emotional heart of their journey in this fic. This fic and Fortress by glasslogic (at the bottom) have similar premises and they 're both fantastic.

Armageddon Game by Alulaspeaks. Rated Explicit, 57k, Wincest. Summary: A year ago Dean watched Sam walk away from the life. A few months later Sam dropped off the radar completely, his last words to Dean a scribbled note. I just need some time. Don’t look for me. I’ll call if I need you.
Now it's 2009 and Dean finds Sam locked in a warded cell, guarded by the Campbells. They say he's running with demons, that they call him the Boy King. They say Sam's up to something big. Dean and Bobby confront a caged Sam who is cold and distant and far too knowing. While everyone tries to tell Dean that the brother he knew is gone, Dean is determined to find the truth. Along the way he discovers angels, broken seals, a runaway apocalypse, and visions of another timeline that burned up his brother's brain.
Now all Dean has to do is figure out what Sam's endgame is and how to stop it, or risk losing Sam forever.
https://archiveofourown.org/works/12684375
I loved smirky maybe-he's-possessed Sam in this. What a great effect to start out with. The clue paths and slow reveals were excellent in this. Love the love between Sam and Dean in here too. Great fic.

Fortress series by glasslogic (AO3). Rated NC-17, Sam/Dean, 225k words. Summary: Seven years ago Dean Winchester paid his due to the Crossroads Demon and fell into Hell. Grief almost killed Sam, a demon blood addiction came closer, but he rid himself of demonic attachments and spent years building himself a prison where no demon can set foot, determined to take himself out of the apocalyptic game that had crushed his family. But each year on Earth is an eternity in Hell, and now Dean is back. Angry, powerful, and demonic; he has a plan to wreck vengeance on those who destroyed his life. A plan that will shake the foundations of the Pit and send shock-waves into Heaven. Dragging a reluctant Sam in his wake, will Dean manage to pull it off before the combined legions of Hell get their act together enough to stop him
ao3.org/series/20086
my thoughts: my thoughts: A super well-written, dark version of Demon!Dean where his ‘evil ' nature and his ‘good ' goals (and kind of amoral adoration of Sam) are balanced. It was satisfying to read Demon!Dean saving Sam from Ruby but warning there 's a lot of rape-or-die to that whole thing. Not a lot of tender shmoop but I really enjoyed this story. Quality, edge-of-your-seat plot progression (using seasons 4 & 5 as a basic road map)

Lost Time by dimeliora. Rated NC-17, Sam/Dean, 171k words. Summary: Sam Burton has an average life, a foul-mouthed sister, and a dream of putting his past behind him. All of that changes when Dean Winchester comes to stay.
ao3.org/works/686421/
my thoughts: An incredible, epic love story, with season 4 intertwined into it. I adored this OC named Ophelia, she was actually like the standout character for me (she had a few lapses of "the cool girl" in her but otherwise I loved her!). But I think what I loved most was the slow burn in the first like 50% of this story. The rest was great but I was so invested in how Dean could come to care for Sam when he was initially so resistant.

Afterimage by paleogymnast. Rated NC-17, Sam/Dean, 27k words. Summary: "If you had it to do over again, and you could change everything, would you?" When all appears lost, Dean Winchester—battered, weary, guilty, and alone—is given the opportunity to travel back in time and live his life over again with the promise that if he makes the one choice he was too afraid to make before, he will be able to change the future, and avoid the loss of everyone he ever loved and everything he fought for. But how? After all, he knows time can 't be changed… But with the help of a mysterious entity, who may or may not be the actual God of Time, Dean discovers time can be rewritten.
Armed only with the ghosts of memories from his former life—afterimages of rewritten time—but not really understanding the gift he 's been given, the new Dean, an impossibly young 27-year-old hunter, once again turns to his estranged brother when their father goes missing. But when he takes a chance on forbidden love, will it be the key to saving the universe and averting the apocalypse, or will it only bring about the end even faster?
ao3.org/works/4504065
my thoughts: Holy crap this author 's writing hijacked me the last week of October while I was still trying to churn out a lot of written work). I absolutely loved this story, loved how Dean pressured himself to admit his feelings for Sam during Bugs, how the author described/framed Sam & Dean 's relationship, and plot-wise how information on seasons 4 & 5 filtered into seasons 1-2ish Sam/Dean. It filled me with so much hope & happiness to imagine them besting their destinies like this with the help of Kronos. Also I'm such a sucker for soulmate tropes & loved how paleogymnast let Bobby and Missouri be cool about Sam/Dean. This fic is also in my time travel and soul stuff reclists.

Another Go Round by KassandraScarlett. Teen and Up, Sam/Dean, 21k words. Summary: Someone sends Dean back to 2009, with a mission: change the past, change the present, so the apocalypse never happens. Dean leaves behind a Croatoan-ridden world, only to stumble into the one person he's always loved more than anything else. Or: Zachariah doesn't send Dean to 2014. Instead, Chuck sends the Dean of the future to 2009.
ao3.org/works/23284600
my thoughts: The aaaaaaangst in this one was so, so amazing. I loved how kassandra had future Dean, this savage post-apocalyptic warrior, realize he was in the past, pre-apocalypse, he's got Sam, and everything falls away and he gets to love Sam again. And Sam, how desperate he is during this time period in canon for Dean's affection... 😭😭😭 ugh, this was so good, y 'all. This fic was in my 2020 Variety Pack reclist (tumblr) as well as my time travel reclist