As his fingers shed the warm hues of his Asgardian colouring, Loki pressed his lips into a thin line. If the vivid blue that replaced the familiar, comforting tones of pink and yellow wasn't discomforting enough, Loki could feel the flesh under his skin itch as his fingernails thickened and raised lines emerged over his knuckles. He supposed he ought to have been glad his true form was no longer marred with badly-healed burns, but in truth, even now, every moment Loki spent with his true form exposed left his stomach crawling with unease.

But how much was it costing him to keep his true face hidden day in and day out, year after year, century after century? He had never fretted about it overly much, although for years he had suspected the sustained effort of his concealment narrowed his capabilities. In the past, he had wielded magic enough for his purposes.

The time-travel, however, had left its mark. After hours of trial and error, Loki had confirmed to himself that his magic remained, albeit in a crippled form. The simplest works now required thrice the effort they had taken previously and the more complex spells eluded him entirely. Loki could only hope that this was a temporary problem.

If not, he had to find other sources of strength. His magic, not his tongue or his knives, had kept him alive thus far. Without it, he was dangerously exposed.

Heavy footsteps echoed around the room; he was no longer alone. Loki restored the concealment and mentally chided himself for his stupidity in exposing himself in as public a place as the palace library.

Leaning back into his chair, he called out. 'Thor, I'm here.'

He probably needn't have bothered. It was late in the evening and with no one else about, Loki had extinguished most of the lights. The sole remaining ones were over the central passage and over the desk Loki was working at. Only a blind man would have failed to spot him. On the other hand, it made Loki feel less like a recluse to reach out to his brother so.

'We missed you in the training grounds,' Thor said. He dragged over a chair from one of the nearby desks and slumped into it. 'You must be lost in a very fascinating project; no one's caught more than a brief glance of you in days.'

'Frustrating, not fascinating,' Loki replied.

His words were true enough. He had spent the three days since Thor's coronation buried under piles of books, initially from his own collection, then from the palace library. Yet any answer as to what he could do about his magic eluded Loki. Although this was infuriating, he wasn't surprised in the slightest. That was the risk with dabbling in unproven, theoretical magic. When things went awry, there were no troubleshooting manuals on hand.

Thor wiped the sweat still beading on his forehead, then pushed his dust-coated hair back behind his ears. 'What's this for?'

'Doesn't matter,' Loki said. 'It was just a stray thought I had and I'm starting to think it's not actually possible, so it might be best to just drop the matter.'

'Not possible? That sounds like a challenge.'

Loki chuckled. If he were trying to push Thor towards something, Thor had just given him the perfect opening. Another few words from Loki and Thor could be on his way to slay some mythical beast in the darkest caverns of Muspelheim.

It's almost a pity all I want is for him to drop this topic.

'Magic's not your forte, Thor, best you stay out of it.' Shaking his head, Loki slammed shut the three books he had laid out on the table in front of him. 'What about you? You've been king for three days now, have you insulted any ambassadors yet?'

'Four years it's been, Loki. When will you stop bringing it up?'

'Well, it's not an easy thing to forget,' Loki said. 'Father was already beginning preparations for your coronation, then you go and, in about a quarter of an hour, make such a mess of things that Alfheim was ready to start a war. Spectacular work there.'

Thor bristled. 'The light elves are easily offended.'

'I've always found them perfectly personable.'

'Maybe if you'd made some move to help, instead of smirking and snickering at my misfortune!'

'Believe me, there are some things even I can't set right,' Loki threw back, somewhat startled how easy it had been to stir his brother's ire.

The Thor of his time hadn't been nearly so easy to bait. In fact, that Thor would have been able to extricate himself out of that awkward situation with the elves with a modicum of grace, not dig himself in further until he had insulted not only the ambassador's wife, but the entire nobility of Alfheim.

This, infinitely more than Thor's hair or his eyes, made obvious the vast chasm between the man Thor had been before his exile to Midgard and the man Thor had become before Thanos took him. But what had been the price that accompanied that personal growth? High, far too high. Yet Loki had to wonder, if he did manage to change things enough – sparing Thor, himself and everyone around them even a fraction of the pain the coming years could bring – what would be the trade-off?

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Stop it. You've already knocked out the first variable; second-guessing yourself now is a waste of time.

Thor rose from his seat and Loki was about to bid him farewell — Thor preferred to fling about furniture, not words, so this was about the place Loki expected Thor to cut off their discussion. But Thor didn't leave. He watched Huginn and Muninn dive down from the library's vaulted ceiling and circle the room, cawing in tandem.

'We're under attack,' Thor declared.

And he was off before Loki had a chance to give voice to any of the questions on his mind. Recovering from surprise, Loki followed his brother out of the library, through two public halls, along several corridors and then down into the bowels of the palace.

At the entrance to the Weapons Vault, they nearly stumbled over a guard lying motionless on the ground. Crystals of ice covered every inch of his skin and the ground around him.

'Frost giants,' Thor muttered.

Is this the Norns cackling at me?

While Thor stepped over the guard and strode towards the open doors to the Weapon's Vault, Loki's gaze lingered over the frozen corpse.

'The guards work in pairs,' he said. 'Where's the other one?'

The only answer he received was a familiar whirring, which sent the floor vibrating. Loki ducked down just in time to avoid being struck in the head by Mjolnir, but Thor seemed oblivious to his near fratricide. Mjolnir aloft, he burst into the vault.

By the time Loki caught up to his brother, a frost giant lay dead on the floor. Unfortunately, his two companions seemed in perfect health and they had the second Asgardian guardsman cornered, the man's back pressed against the pillar that held the Casket of Ancient Winters.

Thor took down both frost giants with a single swing of his hammer, but rather than looking relieved, the guardsman's face paled.

Loki whipped around. At least half a dozen frost giants now stood at the vault's entrance.

He drew his knives and charged towards them. From the first moment, he felt he was on the back foot in this fight — they were all taller than him and their ice-forged weapons offered them a longer reach. Loki tried to get in as close as possible, so that their long limbs and swords would become a hindrance, not a help. But the tallest of the frost giants caught his arm and swung him around, sending Loki into an unused niche of the vault.

'How'd they get in here!' Thor demanded. He was doing good work with the hammer, although the enclosed space limited the range of his movement. 'Did Heimdall let them through?'

Loki scrambled to his feet and launched himself at the frost giant closest to him. He found a gap in the giant's armour, sinking his knife deep into the flesh above the frost giant's hip. Loki staggered back. An injured opponent wasn't a dead one.

Besides, Thor was right, they needed to find how the frost giants had gotten into Asgard. Loki's knife found its target in the neck of another giant as Loki forced his way out the vault. Making sure to keep his knives raised should someone attempt to engage them, Loki skirted around the dead guard and took a more thorough look around.

He swore when he spotted the portal. The pillars along the passageway hid it well, it was no wonder Thor and Loki had missed it on their way in. But this portal was at the exact spot he had intended to open one during Thor's coronation.

This shouldn't be happening.

Someone struck him across the middle of his back with enough force to send Loki skittering forward a foot. He swerved around. A frost giant grabbed Loki's right arm and wrenched it counter-clockwise until Loki's grip slackened. The knife in his hand slid out, clattering along the flagstones.

'Look,' the giant sneered, 'I've caught myself a pretty princeling.'

Just as Loki was about to make use of his other knife, a second frost giant caught his left hand. This one, a female, grinned and pressed her fingers tighter around his forearm.

Oh no, no, no. Fuck.

Even through his thick shirt, he could feel tendrils of frost spreading out from the frost giant's hand out over his own skin. There was no need to look down either. The confused expressions of the frost giants told Loki more than he wanted to know.

Thor leaped out the doors to the vault with a furious roar. Not a second later, the doors were flung off their hinges and torn into pieces in a torrent of ice.

Loki recovered from the shock of seeing the Casket in use faster than the frost giants. He head-butted the female one, breaking her nose. Her grip on Loki loosened, so Loki twisted out of her hold and stabbed the other frost giant in the thigh. This was hardly a fatal stroke, but it allowed Loki to slip away.

Meanwhile, Mjolnir whistled through the air, sending chunks of blue and white ice flying in every direction. Loki could barely see the frost giant currently wielding the Casket amid the furore. Nevertheless, he couldn't stand idly by — this wasn't a weapon Thor could deal with on his own.

Loki lunged forward. Just as he did so, Thor altered the direction of his swing, throwing off Loki's calculations. Loki had to awkwardly dive sideways to avoid his brother's wrath and landed far further from his target than he would have liked.

'Oh, thanks, Thor,' Loki muttered as he clambered up.

He struck out at the nearest target available — the giant's calf.

The frost giant howled with pain and swung the casket down. Throwing his arms over his head, Loki rolled away. Just as he prepared himself for the Casket's full force to come down on him, the torrent stopped.

Loki lowered his hands just enough to see what's happening and found Thor standing over him with a satisfied smile on his face.

'He's dead,' Thor said, offering his hand to Loki.

The frost giant was indeed dead; anyone would be after Thor swung Mjolnir into their head. Loki cringed at the bloody sight, but he had to admit this had been the decisive stroke of this encounter. The Casket lay idle beside the frost giant's body and the three frost giants who still remained on their feet turned to flee.

Loki brought his hand up to close their portal. But when he completed the incantation, nothing happened.

One of the giants slipped through to the other side.

'Close the portal!' Thor hollered.

The second frost giant reached the portal. Loki tried the spell-work again. The result was the same. The remaining frost giant jumped into the portal and disappeared from view. The portal's glowing edges pulsed, then rolled in until the portal was no more.