I've been digging through Avengers fics focused on Thor and Loki and I was actually kinda surprised nobody seems to have used this premise already. (If someone has and I missed it, I'd love to check it out.) Enjoy! And maybe keep some tissues handy.

"You listen well, Brother," said Thor, pointing at Loki with Mjolnir. "I may have spent the last year grieving, but I will not allow you to bring harm to Midgard. Whatever quarrel you have is with me, not this realm."

"Whatever quarrel I have?" said Loki, looking incensed. "I thought I'd made my grievances quite plain not a moment ago, but you seem to think them nothing but fancies! More fool me for voicing them in the first place. I should know by now not to waste my breath." He turned his back in disgust.

"What grievance?" said Thor angrily, grabbing Loki's arm and wrenching him back around. "'Tossing you into an abyss'? That never happened! You let go!"

Confusion briefly registered on Loki's face before his features twisted into a snarl. "You think I will believe such a pointless lie?" he said, shoving Thor away. "I was there! You stole my victory from me, jealous that I was the one sitting on the throne you'd thought would be yours, and then, unable to abide the idea that I might have become more than the meek shadow trailing in your wake, you threw me from the bridge to be rid of me for good!" Angry tears shone in his eyes, while the look in them dared Thor to challenge his words.

Thor stared at Loki in horrified bewilderment. He'd never been very good at discerning when Loki was lying, but the betrayal and rage looked and sounded entirely genuine. It seemed he truly believed Thor had tried to kill him—his baby brother, who had often come running to his chambers after nightmares frightened him awake when they were small, who had fought at his side for centuries, who had been his dearest friend as long as he could remember…whose absence the last year had been like living with a gaping hole in his chest that refused to heal.

All of his own anger and hurt at finding that Loki still lived but had chosen to attack a defenseless realm instead of coming home to those who loved him fell away, and his throat tightened painfully. "Loki, no," he said, his voice breaking a little, Mjolnir falling back to the ground. The details of that night—the worst night of his life—were still crystal clear in his memory, and he'd passed many a listless hour since torturing himself with pointless thoughts of what he could have done differently. "When the bridge shattered, it threw us both up into the air. You were still holding Gungnir and I managed to seize the other end, and Father caught me by the ankle before both of us could fall into the collapsing Bifrost. You told Father you'd done it all for him, and I just hung there, as useless as if I was still mortal, trying and failing to understand how everything had gone so wrong so quickly. I could've pulled you up and gotten a good grip on you, but I was too slow to think of it. And then, when Father voiced his disapproval of what you'd done, it was as though something broke in you. I saw the decision forming in your mind and I begged you not to do it, but before I could force my limbs to move, you had let go. I watched you fall until the vortex swallowed you from view."

Loki's breathing had grown more and more rapid throughout Thor's recounting, and the look in his eyes was wild. "No. You're—you're lying."

Thor chuckled. "You know I was never the one who had that skill," he said gently.

Loki stumbled backward, shaking his head. In his distraction, he failed to notice the edge of the cliff they were standing on. His left foot slipped and he let out a yelp as he began to topple over the edge, but Thor lunged forward and seized him by the front of his black and gold surcoat, pulling him back onto solid ground. "I should have done that a year ago," he said. Loki's hands had found Thor's forearms in an effort to steady himself, his breathing still erratic. "I do not deserve your forgiveness for failing to act then, but know that never again will I let you fall."

Loki stared at him, his gaze flicking back and forth between Thor's eyes. "You...you speak the truth," he said, his brow furrowing. He looked so confused and lost, and it made him appear more like a lad not yet seven hundred than a man just past his first millennium. "How can that be?"

"I fear something has been meddling with your mind since you fell, twisting it so that you would believe I counted you my enemy." For the third time on this clifftop, Thor moved to grip the back of Loki's neck, and he looked him directly in the eyes. "It is not true. You are my brother and my friend. I may not have always been the brother you deserved, but never doubt that I love you." He smiled.

Loki's eyes were bright with tears again. "Brother...," he said, and Thor's heart leapt. Perhaps there was hope for him yet. Before either of them could say or do anything else, however, something very solid barreled into Thor from the side at great speed, wrenching him away from Loki and knocking him clear off the cliff.

Based on how incompatible Loki's "freedom is a lie" rhetoric is with the fact that he is the God of Mischief and his megalomania is with "I never wanted the throne!", how unwell he looks in the Thor end credits stinger and the beginning of Avengers, the "he will make you long for something as sweet as pain" scene, "You lack conviction.", the fact that Thanos was in possession of the Mind Stone before lending it to Loki to help him take over Earth, and what Loki does with both the Tesseract and the Aether in the intervening years between TDW and IW, I'd say it's practically canon that he was tortured, manipulated, and brainwashed into being Thanos's goon, but snapped out of it somewhere between getting Hulk-smashed and Ronan killing the Other. In which case, it shouldn't be impossible to get through to him if Thor only has the time and opportunity to do so. (The battle of New York is a bit late in the game for that, but I love that Thor still tries.) I think the only reason Loki never speaks up about what he went through is his pride. He'd rather be seen as the villain than a victim because he doesn't want to be thought weak (and he hates himself, so he doesn't want to be forgiven), but he fails to realize that asking for help when you need it is not weakness and villainy is not strength.

Anyway. I wrote some of this while I was at work, and the bro feels were so strong that it became very difficult not to dissolve into a sobbing wreck in full view of my coworkers. So that was fun.

Was super happy to incorporate a line from one of the many deleted scenes from Thor that should've been left in (or reworked a bit and then left in). They cut all the scenes where adult Loki smiles! That's not okay! The final cut of the movie makes him look like such a sour child, but this is the God of Mischief! He's supposed to be having fun! What is this nonsense?

Regarding the title of this chapter, I've seen a lot of indignation in the Loki fandom over the "imagined slights" line, and I'm not sure why, because it seemed to me that Thor was specifically referring to the blatantly inaccurate "I remember you tossing me into an abyss," not Loki's entire life of being Asgard's least favorite prince. Thor is a giant puppy who loves his brother and maybe took it too much for granted that all was well there, but after his character development in the first movie, he wouldn't just dismiss Loki's grievances out of hand if Loki ever explained them, but they never get a chance to talk about them before Loki's actions severely complicate matters. (Also Loki, as previously mentioned, has some real issues with being vulnerable with anyone, so it's unlikely he was going to open up to Thor on a whim. His secretive nature is likely why Thor has been able to assume everything was fine up until it suddenly fell apart in the space of a few days in the first place.) And that's the point of this fic.

What is it about the Thor characters that gets me writing essay-length author's notes? I haven't done that with most of my other fandoms.

I do want to extend this to see how it affects the rest of Avengers and the brothers' return to Asgard, but I'm not sure how much I'll be prioritizing this fic compared to my other Marvel fics, which are about to include a co-authored one about how the MCU incarnations of Stakar and Aleta from GotG started out as Asgardian warriors during Odin and Hela's reign of terror. So...we'll see.