I do not own "Avengers." Or "Thor." This chapter takes place just after Thor, and just before Avengers. There are some spoilers for the Avengers.
When Loki fell, it was his magic alone that saved him. Down, down, down, through the cosmos both known and unknown did he tumble, falling endlessly downwards though truly no direction can be gained when there is little difference between ground and sky. As he fell Loki felt his mind slipping from him, his logic and intellect leaving him as he passed Vanaheim and closer to Midgard and bringing him into naught but his emotions.
And it was there that he forgot his teachings and his upbringings, and thought only on the treatment he had received. He had been taken in, without question, as Odin's son. He had been raised as Thor's brother. He had been loved by Frigga, whom he still called mother. He had been trained in the arts of magic and war, and learned on his own the gift of a quick tongue and quicker mind. And he recalled the slights on his name that had been thrown.
He remembered the day he was given title of Captain of the Guard. A lofty title indeed, had it not been out of spite. Thor was to be Captain. He was a better warrior, strong and agile in battle, and commanding the hearts of the men of Asgard already at such a young age. But Odin had proclaimed loudly to all that would hear that Thor was to be taught the ways of kingship, and forgot the title of Captain of the Guard. Thor was angry at first, until it was explained to him that he would not be Captain, but a commander even over the highest of generals. He was the first born prince, and no lowly title of captain would suit him. No, he didn't have time to oversee the guards that kept Asgard safe. He had to learn how to be a king.
So the title was cast off Thor's shoulders, and given to his brother Loki. It wasn't worth Thor's time, and so it fell to the next in line. Loki did his best. He kept his guards from falling slack, kept their honor so they might not shame the great name of Asgard, and did his best to prove to his father that he could be a good son.
And then the Frost Giants came. And while Loki was the one to show them how to get in, he had thought on how it would reflect upon him when his guards could not protect their land. And in trying to gain his father's favor, had lost it when Odin thought Loki to be slacking on his duty as Captain of the Guard. He allowed Loki to keep his horned helmet, his uniform of black and gold and green. But the disappointment was evident. And it had stung, even though it was originally part of the plan. To lose favor, and then to gain it back tenfold when HE was the one to save Odin and Asgard.
But he could not forget the disappointment, and had not thought of what it really had meant to Odin that his adopted son had failed him. An easy task; guard the realm. And Odin thought Loki so lowly that he couldn't accomplish even this. Loki had expected shame on his guards, not on himself wholly. But there it was. His guards, the men under his command with their own horned helmets and garb of black and gold and green received no thought or concern as to their own failure. It was Loki who was given that honor alone. And no amount of work could ever have given it back, for it was at the bridge that Loki discovered that there was never any honor to his name.
Odin had denied him. Not what he was, not what he stood for, not what he tried to do. But him. He denied that Loki could achieve any love or grace. That he could have ever made his father proud. I could have done it father! And in answer was a resounding No. He could have done it. Made his father proud, gained his father's favor, earned the love that he sought after. Could have gained the title of Captain of the Guard rather than simply picking up a cast off covering that Thor had once (almost) held, a hand-me-down with the thought that it was an unworthy title for any son of Odin.
And as he fell past Midgard, and landed, finally, at the roots of Yggdrasil, Loki felt his mind go blank and the shame of his fall left his thoughts. And he sat between the roots of Hel and Jotunheim, and gazed into the empty void that had once held the realm of the Frost Giants. His home land, though he knew the world not. Asgard had been home, but he had been cast out long before Thor had been banished. He was a creature of no world now. Jotunheim was gone, destroyed by his own hand. And he had not been welcome there. He was a runt, even in his Jotun skin, and a traitor to his blood. And he was not a child of Asgard, despite his shape shifting abilities that made it appear as though he was. He did not belong there, not now, not ever. A creature without any proper place. Perhaps Hel, his daughter, could take him into her halls. He was surprised, really, that he wasn't there already.
He was dead, was he not? None could fall from the Bifrost and survive the decent into the void. But here he was, sitting on the very roots of Yggdrasil, and gazing at the realm of his Hel. And at the shattered world of his birth. And he found himself alive.
His born curiosity gave way, and he gazed up, and up, and up, at the trunk and boughs of the Great Ash, and with it his mind left him.
And thus is how the Chitauri found him. Gazing up at Yggdrasil, alive. For none of their kind had gazed upon the tree and survived. But Loki was unwell. His gaze had been held fast by the tree for too long, and his mind had been taken from him. Blood dripped from his nose, his skin was translucent, and his sanity torn by the waves of life the tree had pumped through him.
And so the Chitauri seized his shattered self, and fed the liesmith their need for a realm of their own, and tied their own desires into his need for acceptance. And after eight Midgardian months of gazing at the vastness of Yggdrasil, Loki was easy to bend into any frame one desired.