He’s wondered if it’s something he’d done. He assumed it had to be, but he couldn’t imagine what. He’s spent years wondering, going over conversations, replaying entire days in his mind to search for something he’d done wrong, some way he’d hurt Thor so deeply that it turned him into this dark shadow of himself. And then he too began to change, slowly and subtly, he’d grown harder, honed sharper from the abrasiveness that was Thor now. And yet he’d never stopped trying, never stopped applying that clever mind to this question that he needs to know the answer to, never stopped asking himself what changed.
Then one day it clicked. One day when distance and conflict turned into an argument, when Thor tried to turn a verbal dispute into blows and Loki tried to outsmart him and keep just out of arms reach. It worked without fail, just as it always did, Thor falling for the illusion and getting ever more furious, which is the entire reason that Loki continues to use that tactic on him. But this time, he noticed something. He saw that when Thor finally found the solidity of his body in the trick of false Lokis and gave a push that there was something else going on, something more than indignant fury. His eyes were bright, not with anger, but with something entirely different, pupils blown, pale skin flushed. He looked somehow more boyish and not boyish at all in that moment, as though he were finally seeing the truth beneath all of these years of anger, seeing the man that Thor was desperate not to become.
He knew he was right, but then had not been the time to push and get Thor to give himself away any more than he already had. He had to wait until it wasn’t expected, until he had the upper hand and could tip things in the direction that he wanted them to go. So he waited until one evening when Thor’s friends had left and there were moments to be stolen before turning in. Thor thinks he’s alone, perhaps, as he heads towards his chambers, but then there’s a tap at his shoulder and when he turns to look — because he always does — Loki will be in front of him instead, blocking his path, squaring his shoulders to lord the slight advantage of height that he’s got on Thor over him.
“Something the matter, brother?” he asks innocently, as if he’d just been there in front of him all along, witnessing Thor turning to look at the nothing behind him, accusing him of being jumpy, perhaps paranoid with that tone.
