Came up with this idea after I got sick of people playing apologist for Loki and decided to do a treatment of what, if they do things in Norse mythology style, would happen to him.
Disclaimer: I don't own Thor's Marvel incarnation.
Far from the heights of Asgard, in the deepest pits of Niflheim, Thor stood beside the silenced form of Loki (the liesmith, the murderer, the traitor), and he who was named for the thunder that followed in his wake was so pale that his red-blonde hair stood out like flames upon his face.
Odin and Freya were quiet, like the hush before the storm. Odin's eye was downcast, and his face grim as Thor had ever seen it. He had been angry many times, in Thor's presence, and yet this was something different and frightening. This was a look colder than the Casket of Winters itself, and burning from within with a fearful rage that would shame even the heart of Muspelheim's flames.
Thus spake Odin Allfather to Loki, "I am sorry, for what you have done." And that was all. Not a goodbye, not an apology, but a condemnation of his treacherous son's actions. Freya was colder still; Thor knew that she loved Loki, in her way, but always they had been at odds, rivals to one another. Thor thought of the stories the humans told of the Aesir, and he almost dared to say that the humans knew more of them than they ever suspected.
He almost said that he had already known was Loki's punishment was to be. But that would be cruel, and he swore that this act, neccesary though it was, would be his last cruelty.
Loki was a traitor, a kin-betrayer and who had murdered those who believed in him, allied himself with monsters and those who would murder worlds. Thor knew that it would be best that Tony and Steve and Bruce and Natasha should not know of this (though perhaps Clint would not mind); they were heroes like him, but their cultures were not that of Asgard.
They would not understand the laws, and they would suffer to know what they would inflict upon a fallen foe. Nor would it matter to them that the gravest sin of the Asgardians, of the royal family known as the Aesir, a traitor to one's friends and chosen family was something too terrible to even imagine. It demanded an equal retribution.
Thor said nothing, but the skies screamed with the thunder that had coined his name.
Loki's eyes looked up, wide and moving every which way, beseeching mercy. He would recieve none. He deserved none, and knew it. He had no other way of communication; his body was wrapped tight in a case of metal that looked grown, flowing around his body such that he was pinned and unable to summon his sorcerous skills. Around his mouth was clamped a vise, thin thread slicing into his skin and down until his jaw was locked, sewing his mouth shut. The great weapon of the Liesmith was denied to him.
Thor briefly wondered if Loki, like him, had read and heard the tales the mortals told of them in the places where they were still worshipped and revered and honored; the lands of Scandinavia, Denmark and Norway, and Sweden and Finland and others, and all over the world. Thor wondered if Loki, like him, knew what was coming.
Before them, there was a huge cavern, glowing with lines of eldritch power such that no dimensional breach could happen, no power could open a hole, and seals of such potency that save for the command of Odin Allfather, once this place was sealed, it would never be opened again.
Within it, there was a set of barbed shaped upon a central fame; suitable to take the metal case that bound Loki. Thor took up Loki's still body, forcing himself not to feel Loki trembling and shaking inside, silently screaming and begging for a mercy that he had disowned a thousand times over with every life he had taken for his own amusement or goals, but something in Thor screamed to do something, to break him loose and hide him away and educate him until he was good again-
If he had ever been good. Thor let the notion pass. What could have been, was no longer relevant. Loki must pay for his crimes, and never be a threat again.
With a gentleness that seemed obscene for the occasion, Thor put Loki's imprisoned body against the frames, and they latched to it, holding it tight there. Thor stepped out of the cave, as something moved.
It was hard to say what the towering thing coiling around Loki was; twice as thick around as Thor himself, it's body akin to a serpent's though not flesh nor metal nor dripping ichor-soaked mist almost made solid but perhaps something like all those three things, and it's head was a mere blunt shape, a single red light staring own at Loki in condemnation.
It had a mouth, and from it was a powerful enchantment of Odin's design. Thor felt it pass him, and shuddered as he felt the echoes of Coulson's dying breaths, the ignored screams for mercy from slain frost giants and humans and the hundreds killed during Loki's exile from Asgard before he was found by those… others, and more, so many that they made a single noise like a hammer blow to his brain, a whispering horror that made his skin crawl and want to tear his husk away to silence the knowledge of how many Loki had murdered, all those fates he had cut short by his hand… all that pain, gathered up into a corporeal form, the vengeance of the murdered.
Something dripped from the thing's mouth, this instrument of retribution. It seemed almost like venom.
Thor knew the stories now. He had told Odin not to tell Sigyn, Loki's friend and perhaps once wife-to-be, of this punishment. Sigyn the fire giant, Loki's friend in past years, easily bigger than Loki's own father and with a warm heart to match her size (though a dispostion so serious that Loki had abused himself so to make her laugh, and Thor almost smiled at the memory of how desperately Loki had wanted to make her crack a grin, and he wondered if perhaps Loki might have had a chance if he had bade him to spend more time with the fire giantess instead of lingering in Thor's shadow, but that was another tale). Sigyn, who would have come with a cup to ease Loki's grief, and be sealed away forever until the stars fell and the Wolf and the World-Serpent arose as Loki's maddened children, and then-
Thor did not wish anyone else to suffer with Loki. Even if it eased his pain. No more would suffer for his madness, but Loki himself.
Loki deserved this, and Thor had to remembered that as the retribution engine turned it's attention to Loki, and Loki's eyes wide in abject terror, trembling and wet with tears, and silently they said 'Thor! Help me!'.
Thor thought of Coulson, murdered from behind. He thought of the frost giants Loki would have killed for his childish ambition. He thought of the many Loki had killed, either in person or as a consequence of his plans. They deserved justice, and retribution, and Loki could not be allowed to harm anyone else again.
Even the memories of Loki and him at play, the centuries of comradeship and family, was meaningless compared to the blood on Loki's hands. Even so, Thor leaned in and whispered, voice hoarse like a windy day as dry and dead as the most empty desert, "I'm sorry, brother-" he stopped. "I am sorry, Loki. I am sorry I could not save you from yourself."
The tears fell, and the way they were falling, some might well have fallen upon Loki's brow.
"Please, for the sake of what good there could have been in you… do you honestly understand what you did? Do you even care?" Thor demanded, every ounce of superhuman charisma bleeding through.
Loki, of course, could say nothing. There was wetness upon his tears, but his eyes seemed dry, now. Any tears he might have shed, were reserved only for himself.
"…Goodbye, Loki." Thor stepped away, and left the cave.
Odin and Freya's faces were grim, and though Loki had brought so much trouble to them, they weeped openly. Odin spoke a word, a powerful word, that even Thor's mind could not comprehend, and then the cavern was shut, sealed forever more.
The screaming, even through solid rock and metal and a mouth sewn shut, shook them all, and remained in Thor's nightmares for some time.
