Rec!
Animalia by gyzym. James/Sirius, Remus/Sirius, James/Lily PG-13, summary: Everyone assumed that Sirius and James got on so well because they were exactly alike and they were all wrong; everyone assumed Sirius and James got on so well because they were both crazy and that was true.

I was asked to beta this and... basically squealed a lot and (sort of) flogged her into finishing. The characterization! The Peter-actually-existing! The Remus and his marmalade! The Sirius! I shall include an excerpt to tempt you:

But still, the boy was sixteen, and even if he had grown up love starved and haughty there was no reason to get in brawls before he’d had any marmalade. Not that the marmalade was cursory, not that Sirius could fight as much as he pleased so long as he’d had some delicious orange preserves first, but it was—base. It was base, that’s what it was, it was base and also cruel and James was leaning into Sirius’ ear again and goading him in that way he did and

“Pass the marmalade!” Remus yelped, perhaps with a bit more passion than was required. James twitched, and Peter jumped rather violently, and Sirius turned with one cool eyebrow raised and looked at Remus with amusement that was pleasantly condescending.

“I’m not deaf, Moony, honestly,” he said, and passed it, and added, “bloody hell, but you’re odd in the mornings,” like he was remarking on the weather instead of Remus’s character. And oh, he was maddening, he was smiling showing his canines and doing it again, acting like he was just a little bit better than everyone, and Remus couldn’t make him stop because Remus agreed with him and his stupid aristocratic pride.