Thor loved his brother from the moment he first saw him. Now, that made it sound as if Loki had been born into the family; he wasn't. He was given - gifted - to Thor at the age of fifteen, slender-boned and sullen, a playmate and heartmate after a lifetime of solitude. Thor had long been the only child of Odin Allfather, Minister for Magic, and while he had never lacked for sycophants (and, on occasion, actual friends), neither had he ever been wanted for who he was, lumbering and adolescent and clumsy. He was always Odinson; he was never merely himself.
Loki, though - Loki was his brother, not a follower or a leader, not above him or below him in power or in stature (well, all right, he was rather tiny). Loki was his equal, the only one that could possibly love Thor for everything he was - and wasn't. And if, at the moment, it seemed as though Loki might hate him instead, surely that was only a matter of time, a temporary state of affairs that would resolve itself as Loki got to know him. Family couldn't hate each other. Obviously.
That, and Loki's aloofness had the prickliness of a cat's, a general sort of misanthropy, and Thor knew better than to take it personally. Sometimes, he even found it downright charming; Loki had a razor-sharp wit, and was readier with it than he was with his wand, able to reduce the fat, rich, babbling suck-ups that approached Father into piles of quivering, resentful lard.
Thor loved him for that, too - for how Loki dared to speak to them, when all Thor had ever managed was a strained smile. Everyone remarked on how well-mannered Thor was, how jovial and approachable, but the fact was that Thor was too paralyzed with fear of how he might seem, with fear of how he might disappoint his father. For all that he was a Gryffindor, Thor was beginning to realize, he was a coward; all he was good for was the brawny sort of valor, that earned all of the glory and none of the ignominy.
But Loki, now, Loki was brave - in an especially Slytherin way, the kind that had him face down hatred and malice and cruelty with a mocking laugh and an upstart sneer, and a steadfast refusal to be broken. Hell, it was thanks to him that Thor had realized Slytherins could be brave. Thor shamefully reflected on his own bigotry, that he had once thought Gryffindor the bravest House of all.
"Don't be a twit," said Loki, when Thor told him his thoughts. But an unwilling blush crept onto his face, as though it would've liked to bribe high-ranking Ministry officials not to be there.
Thor couldn't stop a grin from creeping onto his face, and Loki looked as ferociously displeased with it as he was with everything else.