The first time Loki saw them, he had simply glanced into the mirror to comb his hair. But instead of his own chambers, lined with books and magical artifacts, he saw a mountainside under a sunny sky. His brother.
For a few seconds Loki thought he was seeing a prophecy, but the way this other Thor and Loki looked upon each other made him realize that he now had evidence of a theory sorcerers had been speculating about and trying to prove for untold thousands of years: the multiverse. That there were many parallel universes, possibly with counterparts of those who lived here.
The Thor he knew would never look at his brother the way the one in the vision did. Loki felt physically ill with longing at the affection on this alien Thor’s face, at the way he spoke to his brother. Loki had spent all the centuries of his life trying to inspire that sort of look from Thor and had never given up believing that one day he would succeed, but all that carefully hoarded hope was demolished in an instant of seeing its actuality. There was no way to get his own Thor from his current casual bullying and indifferent scraps of affection to this.
And the other Loki wore an only too familiar sly expression. It was different from Loki’s own slyness, somehow; there was no love at its base, no wish to do what was right. Only greed.
As Loki watched the vision, Thor charged some hostile rock giant, trusting Loki to have his back. At least some things were the same. The pair defeated the giant after a short invigorating fight, and then Thor turned to his brother with his face wreathed in smiles and reached to clap him on the shoulder.
That other Loki grinned and pulled Thor closer for a brotherly embrace. And then Loki, watching, shouted a futile warning as that Loki slid a long thin blade into Thor’s back.
The heartbreak on that Thor’s face was more than Loki could bear, having felt its twin too many times, but he could not look away. Thor’s body would recover, he was an Asgardian after all, but his heart might not.
The other Loki laughed and pitched Thor down the mountainside with a well-placed kick.
Then he turned his head and met Loki’s gaze through the mirror. And smirked.
The vision dissipated, and Loki spent the next several hours trying to get it back. His other self had malign intentions. He had sent Loki the vision, there was no doubt, had wanted him to see it.
But Loki failed to recapture the vision, and was left to wonder and worry.
Loki searched through every book he could lay hands upon in his own library, the palace’s, the temple’s. He scrutinized every scrap of speculation about the multiverse. All he found was theory and fantasy, not a shred of proof and no way of contacting any other universe.
He received no other vision. Months passed and Loki’s attention turned to other things. And then there was the uprising on Nornheim, and Loki tried and tried to talk some sense into his wayward brother, and the oaf charged in and started a fight with over a hundred warriors and Loki was only able to save him and Sif and the Warriors Three by conjuring enough smoke that their opponents could not see to attack them, and with seiðr was able to grasp each of his shield-brothers by the wrist and pull them towards an escape route, and of course none of them realized it was him and what he was doing even though he had saved their lives with magic hundreds of times, and he had to expend yet more magic whispering in their ears wherever they were, but eventually they all followed where he led and reached safety and lived to fight another day.
None of them thanked him, of course. None of them so much at looked at or spoke to him. Reinforcements arrived from Asgard and with a legion at their backs Thor and his friends brought Nornheim to heel, and they celebrated with an immense feast.
And after enough mead for him to drown in, Thor began boasting of how he had “fought his way through a hundred warriors”.
Loki should have expected it, but his stomach wrenched and he dropped his gaze to look into his own goblet of mead.
And on its liquid surface, instead of his own downcast expression, he saw that other Loki, looking right at him. Laughing.
It was only a week later that Loki saw that other universe again. The Dwarves were chafing under Asgard’s rule and Odin gathered a council of war. Loki spent hours in the council chamber arguing that they should try diplomatic means first, generously grant Nidavellir a few face-saving concessions and thus resolve the matter without bloodshed on either side, but the only result was jeers, the word ergi thrown around with abandon, and finally Thor accusing him of wanting to deny him the glory of battle out of his own envy.
When Thor spoke those words Loki gave up arguing, as he always eventually had to, and listened to the rest of the planning in silence. Listened to his brother speak with relish of how many they would kill. With indifference to the deaths of the Asgardians who would inevitably fall.
Loki gazed silently into the flickering light of the hearth. Which abruptly gave way to another vision.
That other Thor and other Loki in some dimly lit building of stone, whispering a hasty council. And then the other Loki’s voice, no longer lowered. “There is no need for that. They are all dead now.”
There was genuine horror on that other Thor’s face. “Loki… what have you done?”
“Really, for one with my powers, slaying them all with magic took less than a minute.”
“Loki, there were civilians here! Children!”
“Who would have grown up to take up arms against you.”
Thor ran, Loki trailed indifferently behind him. In a room full of dead persons of various ages and species, Thor fell to his knees and cried aloud his grief at the unneeded deaths and his own brother’s cruelty.
The other Loki watched coolly for a moment, then turned and looked straight into Loki’s eyes. Loki could only stare, transfixed, not caring if those around him thought even less of him than they already did.
The other Loki gave a little world-weary shrug. “Brothers,” he said with an eyeroll. Then the vision dissolved.
When the council finally broke up and everyone else went to feast and get drunk in eager anticipation of the killing to come, Loki shut himself up in his own chambers and stood before his mirror. He saw only his own face - his, not that mocking duplicate’s - with his own room behind it.
“What is it you want of me?” he demanded.
A ripple, and his other self was looking back at him. “Your brother.”
Loki stiffened. “Thor?”
“I rather think we each got the wrong oaf. A pity we can’t trade.”
“I would not give up my brother for anything.”
The other Loki snickered. “My Thor has said precisely the same of me.”
Loki’s eyes widened, incredulous. “Thor? Said that of me? Or rather, of you?”
The other laughed. It was a cruel sound. “Look at you, like a hungry dog offered a bone. You would crawl on your belly to have your brother speak so of you, would you not?”
Loki looked away, lips thinned. The other laughed softly. “I can give you that.”
“You just said we couldn’t trade brothers.”
“No. The shock would likely break the oaf’s mind. But we can trade places.”
“What? That could compromise the fabric of the universes-“
But the other Loki had already cast the spell, and Loki was abruptly alone. In a magical laboratory which resembled his own, but was not quite the same.
Immediately he began to consult the books nearest the worktable, to reverse the spell his reckless counterpart had cast, but quickly he determined that none of them related to whatever forbidden mysteries had been plumbed to effect the switch.
There must have been books consulted. A pile of fresh ashes in the hearth were, Loki deduced, all that remained of them.
Loki remained in the laboratory throughout the night, searching for some clue as to how the spell might be reversed. He found nothing. And dawn found his brother pounding at his door demanding that they go a-questing together. That other Thor, the one Loki would have given the Nine Realms to have at his side.
In a sense, he had.
The younger prince of Asgard joined the council making final plans for the reconquest of Nidavellir with a tranquil confidence that surprised all. They were accustomed to Loki being either earnest, as he argued for safer more cowardly tactics, or melancholy, as they reminded him of how Asgardian warriors did things.
The planning began, and Loki immediately began discussing how he might magically enhance all of their weapons that they might each slaughter more with each blow, or how strategic blasts of seiðr might flush out warriors who had taken up vantage points from which to fire projectiles.
It was not the first time this room had gone silent that all might stare at Loki as he spoke, but it was the first time the silence was not one of pure contempt.
“Loki,” Thor asked with suspicion, “do you mean you could have been doing this for me all along, and never did? What sort of loyalty does that show?”
Loki hesitated only for an instant. “You have at last shown me that you were right, brother. Allow me to demonstrate that I have outgrown my naïveté and am ready to use my magic as it should be used: to aid your valor in battle. Together we shall make all the realms tremble in fear of the sons of Odin.”
Thor still looked incredulous, but they continued to plan their attack and Thor found himself, for the first time in his life, trusting that his brother would help him lay waste to a foreign realm. As a prince of Asgard should.
“I can slay the dragon.” A frown creased Thor’s handsome face. “But his fire might harm his prisoners before I can subdue him.”
“I can shield them with seiðr,” Loki said at once. “They will be unharmed.”
Thor shot him a glance, full of hope and doubt. The doubt tore Loki apart. It still was more affection than he had ever received from his elder brother.
“Thor - brother - give me a chance.”
Thor smiled at him, rested a hand on his shoulder. But the smile was tinged with sadness.
“You are my brother,” Thor said warmly. “I have given you a thousand chances. I shall give you a thousand more.”
Loki swallowed. “I only need one.”
Thor slew the dragon while Loki protected the people the dragon had captured, and the only harm anyone other than the dragon experienced that day was the singing of Thor’s cape. This Thor was so accustomed to having the lowest of expectations of his brother that he carried on as if this simple deed - not letting his protective shields “accidentally” falter at a pivotal moment - were the greatest of feats, and even the mental echo of his other self’s mocking words about dogs and bones could not stop Loki from soaking it up, drunker on Thor’s praise and smiles than he ever had been on mead.
But just as it did in all the tales, his heart’s desire came with pitfalls. Even as he spent the evening luxuriating in the brotherhood he had always yearned for and never been allowed to feel, Loki was forming plans. He would have to tell this Thor the truth. He would travel to all this universe’s centers of knowledge, to Alfheim and Vanaheim and any other realm which boasted learned sorcerers and overflowing libraries. Somehow he would find a way to travel back to the universe from which he had come. Not to remain - he was not strong enough to give up this Thor, not for anything. But the Thor he had known would eagerly ally with an evil version of Loki, and they would lay waste to their universe and any other they chose to visit. Had Loki’s counterpart left matters as they were, this other Thor would have kept that Loki’s mayhem in check, and Loki himself would have done the same to his Thor. Now there was nothing to stop either of them.
Except for Loki, and the Thor his other self had been kind enough to grant him. That other Loki would have a few bloody years of enjoyment, and then that unholy revelry would be halted by his own other self. That other Loki had sown the seeds of his own doom.
In another universe, Loki’s counterpart watched the sentimental fool whose place he had taken through a scrying mirror. He would watch his other self’s quest for the magic that had exchanged their places. In time the fool would likely stumble upon it, he was intelligent when his brains were not hampered by the heart he was so unfortunate as to have. And then he would drag that sentimental oaf into this universe and try to stop the exquisite chaos about to be unleashed.
Loki’s counterpart smiled into his scrying mirror. That battle would be magnificent. It would be the very twilight of the gods.