In the game of garnering power, it was wise to start small and test the resolve of rivals. Thus Laufey set his eyes on Midgard, with its nigh defenseless people, and planned its domination. This would attract the attention of Asgard and possibly plunge them into a war for which they were truly not prepared; a foolhardy move.
Loki Laufeyson said as much, and loudly, before his father's court.
Laufey had him beaten into silence.
So the sons of Jotunheim invaded Midgard and, as expected, the hosts of Asgard came in brilliant flashes of color. The battles were bloody and mortals quaked from afar, certain the world was ending. The Jotnar were stronger than the Aesir in brute strength, but the soldiers of Asgard were better trained, fighting as a unit as well as in melee as necessary. The Frost Giants were holding their own, but Loki knew it was only a matter of time before his people were beaten, and both would suffer severe losses in the meantime.
It was with ease he snuck into the camp of the Aesir. A cloak and his small size would bring no suspicion, and he was within sight of their king's tent before he allowed himself to be captured. The guards took him where he needed to go, and soon he was standing before Odin All-Father himself.
Loki had heard that the Aesir did not age, thus it was a testament to Odin's longevity that he looked an old man. Yet he radiated a power that left even Loki speechless for a brief time. In the face of such power, it was wise to remain polite, and he tried to bow as best he could when held between two guards.
Odin knew his visitor could be none other than the eldest son of his enemy, his small stature was proof enough, for who hadn't heard of Laufey's shameful runt? Looking at him now, Odin suspected there was more to it than that. Loki was not merely a small Jotunn. The planes of his face were softer, his stance more graceful, and there was dark hair upon his head. In the veins of Loki flowed more than Giants' blood, though Odin could not discern what at that moment.
It did not matter; Loki was the son of a king and would be heard.
Recovering his wits, Loki made use of his silver tongue, honed from a lifetime of surviving among those stronger than himself. He entreated Odin to understand his people and their desire to expand beyond their own realm, much as the Aesir, Vanir, and even Alfar had done. It was hardly the fault of the Jotnar that they required certain environmental needs for their colonies. Surely an agreement could be made, as Midgard was vast and the mortals few in number this far north.
Over the course of a day and a night Odin and Loki drew up an agreement, though it was hardly smooth in the making. More than once, Loki lashed out with his sharp tongue and Odin returned it with a strike from his spear. The Jotnar could establish their colonies on Midgard without interference from Asgard, so long as they remained far from the humans and brought them no harm. To this Odin agreed and left his mark upon the parchment on which their agreement had been written. Loki would take it back to his father and if Laufey agreed he would leave his mark in turn before returning it to Odin.
So Loki returned to the temporary fortress of ice and stone where Laufey dwell and presented his king the parchment. Seeing only benefit in it, Laufey left his mark upon the agreement and had a messenger return it to Odin, ending the war.
Laufey had Loki strung up outside the fortress to be gnawed upon by wolves for a full turn of the moon.
Peace could only last so long. Satisfied with his numbers and the power of the Casket of Ancient Winters at his fingertips, Laufey advanced through Midgard. Again the Aesir came and the war was waged anew.
Loki cursed his father and the Aesir both before departing Laufey's court and finding his way into Odin's presence once more.
"It is too late for treaties, this time," Odin said to him in the warmth of his tent.
"Dragging out this war is pointless for both sides. It must end." His brother Byleistr had been lost in the confrontation mere hours before.
Odin was resigned, but stood firm. "We must protect Midgard."
"Damn Midgard!" Loki yelled, "You must strike at the very heart of Jotunheim! Laufey will have no choice but to return, and there you shall cripple him."
Odin regarded the young prince, his blue eyes as hard as the ice he now battled. "It is not easy to trust one so willing to betray his people. What do you take me for?"
"I do this for my people!" Loki cried, desperation in his voice. Swift as a serpent, he lashed out his hand and, quicker than Odin could draw his blade, grasped the bare skin of the All-Father's arm. He watched as the marked blue of Loki's own visage was swept away, like sand blowing over stones of a beach, and replaced by smooth, pale flesh. No more did a Jotunn stand before him, but an As like himself.
Slowly, his now green eyes wary, Loki lowered himself to one knee before the All-Father. "And in doing so, I can never return to them."
So the battle turned to Jotunheim. Odin led his forces, crashing down upon the planet's surface via the Bifrost, while Loki guided small contingents through the pathways between the realms, flanking Laufey's warriors and leading them into the citadel itself.
The war ended swiftly then, with Odin now One Eye casting down Laufey who had no choice but surrender. The Aesir would take the source of the Frost Giants' power, the Casket. There was no stopping them, but Laufey could take small satisfaction in the fact that no Asgardian could touch it without harm. Thus he was dumbfounded when one of Odin's warriors, a horned helm upon his head, carried forth the Casket as if it were nothing and presented it to Odin.
And Laufey screamed in rage when he recognized this soldier as his eldest son in the guise and armor of the Aesir.
Still bleeding, the surviving warriors collected their dead and departed the fallen city of the Jotnar, gathering where the Bifrost would take them home. Riding beside Odin was Loki, the Casket of Ancient Winters clutched in his hands. As the multicolored beam of the Bifrost descended, he turned for one final look at his ruined homeworld.
Try as he might, he regret nothing.
The citizens of Asgard crowded the streets in never-ending throngs as the victorious soldiers of Odin their King marched from the Bifrost, deafening them with cheers louder than the screams of battle. Thor stood in the golden hall, straining against his mother's hands and waiting for their approach, wanting nothing more than to run out and meet his father. He couldn't believe how far the bridge was from Gladsheim and how slow they were moving and why it was taking so long!
After an eternity the All-Father arrived in his hall to the cheers of the most prominent lords and ladies of his realm, followed closely by his generals and most noted warriors. Ascending to his golden thrown, he faced his family, and Thor could hold back no more. He dashed into his father's waiting arm, hugging him fiercely and fighting back the tears. He was too big to cry. Odin returned the sentiment and quickly gave his beloved son a kiss on his forehead before standing to his full height, his spear Gungnir held above his head in victory. Again, the assembled Asgardians cheered their king and heroes.
Odin raised his free hand and the hall grew quiet. He spoke, his voice carried beyond the walls of the hall itself, of their victory, of the courage and valor of his soldiers. His generals and most prominent warriors knelt before him and he spoke of them in turn. Thor was familiar with them all, and noted those who were missing. He was sad and yet also gladdened, knowing that those brave Aesir had been carried in glory by the Valkyrjur to Valhalla.
One of the warriors kneeling before his father was unfamiliar to Thor. He was not merely a soldier risen in the ranks nor being praised for heroics, Thor did not recognize him at all. Even more strangely, he did not look like any other soldier Thor had seen. He was slighter in build, nearly dwarfed by Tyr kneeling beside him, his face young with a soft jaw line. And yet he wore his golden armor as proudly as any of the generals, the great horns of his helm setting him apart.
Entranced by this strange soldier, Thor missed most of his father's speech, until Odin stepped forward, gesturing for the newcomer to rise. It was then Thor realized in shock that the warrior carried no noticeable weapon. How could he have gone into battle in such a way?
"...due to the personal sacrifice of Loki that we are victorious..."
Thor made a face. What kind of name was Loki? It was no more familiar than the warrior's face. Maybe he had come from one of the other realms. His train of thought slammed to a halt as Odin bade Loki to stand beside him and clasped their untreated, bloody hands together, mingling their blood. Thor gasped; he knew the meaning of that gesture all too well.
Facing the crowds, Odin raised his and Loki's still clasped hands for all of Asgard to see.
"Let it be known that Loki is a brother of Odin forevermore!"
There was the slightest hesitation before those gathered erupted in cheers. Thor only stared at the mysterious soldier from far away. He was very young, but he knew that this was not and honor bestowed lightly. The warrior Loki knew this as well, judging by the look of shock he was trying to cover.
Whoever he was, Loki had earned the highest honor among the Aesir. He had garnered not only the favor of the All-Father, but his trust and admiration as well.
And Thor, unable to look away from this golden warrior, felt nothing but awe.