Loki wasn't certain what it was that made him return.
By all accounts he was free. Free in a way that he never had been before. Free of Asgard, from Thor, from everything that judged him and reviled him and made him seethe and rage and scream inside. He should have been happy. He should have set out, free, without looking back.
Though if pressed, he knew exactly what made him turn back. Frigga- no, his mother was dead, and even though he hated (loved) Odin, he couldn't turn his back at this moment. Perhaps because his hate was equal to what his love had been and, despite how he may try, he could not feel indifference enough to stay away. Perhaps because the only thing that he felt more than his hate(love), was respect, and above even that the truth that centuries of connection cannot be erased simply because he wanted them to be.
He would let Thor think him dead, he was still angry at Thor for reasons that had little to do with learning his heritage and everything to do with the centuries they had shared, but it was, perhaps, time he spoke to Odin.
He moved unseen into the throne room and Odin sat up straighter upon the seat almost immediately. He slammed Gungnir upon the ground once, the sound echoing out among the hall, causing all to fall silent so that he may speak. "Leave me," Odin called out. Without question, but with much curiosity, those in the hall emptied.
"It seems that I am haunted," Odin said, though Loki did not reveal himself nor did Odin look in his direction. "I feel the presence of one thought to be dead, though as I have wronged him, I would not be surprised to learn he wished vengeance upon me."
Loki stayed still, not truly decided upon what he wanted to do. Odin looked weary, more than he had in any of the times Loki remembered seeing him and he took the time to ponder what his father might have suffered over the last two years. One son banished and returned, one son dead and returned and dead again, a wife dead (who would not be returned). Odin was weary and Loki did not think that that was good for anyone. Not Asgard, not the nine realms, and not Loki.
"I have lied to my sons for far too long and I have failed them utterly. I let one son run wild while the other struggled to take up my slack reigning him in. My tongue has never been as sharp as my blade, though I pretend it to be. It is long past due that I admit to my mistakes of which there are many. It is long past due that I beg forgiveness, even when I do not deserve it." Odin paused and Loki could see what he thought might be a tremor run through him. "Am I to be haunted? Or am I to be dead?"
"Neither," Loki sighed, revealing himself and moving to stand before the throne. "I am not here because I am forgiving of you."
"Your kindness has been used up I wager."
"Yes." Loki said simply. It had been too long since he and his father had exchanged simply words. Though he was at times loathe to admit it, Loki shared much with Odin. Everything was a game to them, something to be manipulated, though they worked toward different goal. Neither father nor son had had many moments of open, straight forward honesty, hiding it behind various forms of pretense or being slyly duplicitous in the name of whatever games they were playing.
Thinking of it now, Loki should have known. He should not have trusted Odin when he knew the man to play the same types of games that he did. Odin had never counseled him in tricks per say, but there was a certain amount of teaching by example. And so many nights that he regretted now, felt utterly foolish for, when they would sit together in the night staring out over the edge of the Bifrost and… talk. Confession and confidence and encouragement that made him feel sick to think all lies. Bile and a broken heart, that is what thinking about Odin got him. How could he bare, how could anyone bare, to call such a relation 'father.'
Thor had been oblivious to all the sleights and harm he'd done to Loki. His mother, while implicit in the lie, loved him more than enough to make up for it. Nurtured him in the ways that Asgard always sought to unmake him. Healed him of all the damage done to him trying to please, to serve, Asgard and it's king. Soothing the pains he caused himself on his father's command.
(Loki did not really know if Odin was unforgivable, but it made him feel better to think so. Made him feel to weak and vulnerable to think that he could forgive someone that had treated him so poorly.)
"You committed crimes against Asgard, boy," Odin said, seemingly unrelated, but Loki knew better. Odin, like Loki (not Loki like Odin, never that), did not have a still mind. Everything moment was an opportunity, every action a trick, every word a lie. "What am I to do with you?"
"Mother is dead," Loki said, ignoring Odin's words and saying what was most plaguing him. Not because he wanted comfort (not that he would admit to) but to hurt his father as he was hurt. "Why did you not protect her?"
Odin looked absolutely struck, but it didn't soothe anything in Loki. If it was at the expense of his mother, it would never soothe him to see his father feel as he did. That did not mean that he wouldn't take the blow, however. Bitterness was bitterness after all.
"Is there even anything left of you, King of Asgard? If I haunt you, then what must she—"
"ENOUGH!" Odin shouted, and Loki was horrified to hear his father close to tears, to hear his voice break in the middle of the word. "Enough," Odin repeated in a much quieter voice. "Anything else… you may say anything else, boy, anything else to me or of me, but I cannot bear this wound. It bleeds too heavily for the salt you pour."
'Cannot,' Loki thought. 'Not will not.'
"What will you do with me, All-father?" Loki questioned. "I am a twice dead son-of-no-one. Usurper and war bringer."
"I know the truth of you, Loki. You cannot use the lies of others to do your work for you. If you want me to hate you, you will have to work for it. If you want my forgiveness—"
"I do not need it!"
"Then you need only ask," Odin finished, ignoring the outburst. "And regardless of your opinion on the matter, you are my son. You will not believe my claims of love to you, though I make them, but if your mother were here, she would bid me keep you, and so for her…" His words trailed off a long moment. "It is not about either of us, but for her…"
'And now neither of us has to apologize.'
Loki let out a long sigh, still filled with frustrated, sick feelings of hurt and confused love. Quietly, matching Odin's tone, Loki repeated, "What will you do with me, All-father?"
Odin seemed to take a long breath as well, before sitting up as straight as he could, eyes boring directly into Loki's. "For your crimes Loki Odinson, I cast upon you a harsh judgement. For my son whom never wanted a throne, for my son whom always only wanted to establish his own sense of self, I take from you both these comforts. Your punishment, Loki, is to take up my throne as myself and to guard the nine realms until such time that I or your brother are able to reclaim it."
Loki paled slightly and something tight was in his throat. "Father-"
"I am tired, Loki, and I wager that you are, too. You do not need to suffer all that you feel if you only labor under my disguise." Odin rose and Loki looked away, feeling something uncomfortable rise within him at the words. Loki was dead, and so too, could be all that Loki felt. Loki was poisoned and he was also dead. Lost to bile and heartbreak. Lost in the wastelands of Svartalfheim. Lost and dead and empty. Odin walked slowly down the steps to stand before Loki. "This is all that I can do, Loki. No one will challenge you here."
Loki looked up, wanting to be more angry than he felt. Odin was doing this for himself, as he always did. He was weary and he wanted to give his throne away to whoever would take it. (And Loki ignored the voice that reminded him of Thor, whom could have still given the throne to, but instead was choosing Loki.)
Odin seemed to read Loki's thoughts on his face ("I know the truth of you, Loki.") for he spoke again, quietly, "This is your punishment, Loki."
And Loki latched onto that. It was not love, not affection, not the strange warped kindness that he and Odin shared, it was a punishment. It was not release and refused to admit that it felt like that and forgiveness both. Odin held out Gungnir and Loki was slow to take it. When his hand was wrapped around it, Odin tugged him swiftly into a fierce embrace and Loki couldn't bring himself to move to embrace his father in return nor to push him away. It was all he could do to hold back tears, but his father seemed unable to do the same. Loki tightened his hand on Gungnir. The embrace felt like mourning and he wasn't ready to mourn. (Would never be ready.)
"I am not forgiving you," Loki said, because he had to say it. He couldn't forgive Odin. He was too angry, still, and didn't know where he would put that anger if not upon the man that was embracing him so firmly. (Except he did know. It would go to Thor and that was worse.)
"No, you would not," Odin replied. "But it is good that you came back Loki."
Loki was the one to say the excuse this time. "She would have wanted..."
"Yes," Odin agreed, nodding, and nothing in his grip lessened.
And Loki knew that this was a mistake the minute he let a tear slip. Because this was all so tenuous and he was about to be alone. Thor thought him dead, his mother was dead, and Odin was about to fall into the Odin sleep. He could feel like he felt the strength of their shared grief. Loki was about to be alone and anything could break this moment and everyone after it to pieces.
(And later, once Odin was hidden away in his sleep and Loki was disguised and upon the throne, staring at Thor through hidden eyes; when Thor would ask to leave and Loki wanted nothing more than to forbid his brother from going so that he could keep Thor by his side and not be alone, he would let him go, because he wanted Thor as far from as possible when the walls came crashing down on him. Because Loki was still angry and Loki was alone and Loki never did learn not to throw stones.)