The Marauders had grown up together, faced the world together, graduated together. To Sirius the other Marauders were dear friends and family, and he could never imagine that changing. Until the moment when one of them betrayed everything they stood for. Until, that is, Prongs and Lily had a baby.
Sirius didn't see James for weeks at a time; he and Lils never came out for a drink (or eighteen) any more; instead they invited him over to dinner once a month (a month!) and tortured him with baby stories. Relentlessly.
"No, I get it, Padfoot, you have your own things going on," said James midway through one such night, apparently recognising Sirius' utter despair, "and weren't you going to tell me about - oh! That reminds me. Hey, do you know what Harry said the other day?"
"What?" Sirius forced out through clenched teeth.
"He said daddy! Or, well, he said 'gah gahhy' but I think he was trying for daddy, you know?"
Hours later, when Sirius escaped the interminable discussion of What Harry Did Today, he was surprised to discover how angry he felt at James. Angry, upset, betrayed.
Hours later again, Padfoot, Moony and Wormtail sat over a table littered in empty glasses. The bar around them was poorly lit to disguise the shabby décor, and smelt of old beer. It was more homelike than home.
Padfoot leant forward. "Look - you know Harry's great - but Merlin! If James tells me *one more* bloody story... Look. No. Listen!" He waved his arms, attempting to convey the seriousness of his position. "How about - we prank James? Seriously, I've got to do something to work off the rage."
Peter said, without enthusiasm, "Okay, say we agree. How? I don't want to piss them off too badly right now; you know they haven't been sleeping too well. And don't you think we're a bit old for that?"
Remus leaned forward, eyes sparking. "I know - but I agree with Sirius. What if we just set up the prank to go off much later? I recently learned where the goblins keep the quill that determines inheritance. It's not kept in the vaults, but up on the level with the tellers. If we got in, we could probably tamper a bit. You know, make Harry the heir to some made up family."
Peter frowned. "Isn't there strong security on the quill?"
"Yeah, but I'm willing to bet it's mostly to stop you from changing who inherits into existing families, or to stop you creating new families with the same name. After all, how strongly can you guard against people making up *new* families? There has to be a protocol for it, because muggleborns are adding their names all the time."
Sirius started gasping with laughter. "You - hah - you know we're going to have to borrow his cloak for this! We can even tell him it's for a prank! And you know we can make Harry the heir to so many houses, like -"
"No," said Remus firmly, "I'll help you make Harry the heir to *one* more house. Think about his feelings when he grows up."
It took some convincing, but eventually Sirius agreed.
They broke into Gringotts the next night. Dead easy with wands, and safe too, so long as Remus was careful to stay between Sirius and the entrances to the vaults and patiently explain that no, they couldn't go ride on a dragon. Now all they needed to do, Remus thought exasperatedly after the third time he had to dissuade Sirius from trying to crack open the Black vault, was actually move on and curse the stupid heirloom quill.
"Me nasty goblin, you stupid wizard," yelled Sirius loudly from behind one of the goblin teller's desks, jutting his hips back and forth.
"Hey," called Peter from the entrance, "I brought a few souvenirs with me - enchanted tripwire and a powder that'll raise welts all over. The question is - which one do we put on the main entrance, for humans, and which over there for the goblins?"
"Can we finish up and go home?" said Remus plaintively.
"Oh, you're such an old woman," Sirius called back dismissively. He then turned towards the administration offices, completely missing Remus baring his teeth and growling softly. Well, thought Remus, turnabout is fair play. What if...
"They did *what*? snarled James to Remus over dinner. "Why didn't you stop them? No, sorry, I know that's not fair. You're not Sirius' keeper, and Peter would follow him anywhere. Just... argh, why would they do that?"
"I know," said Remus quietly in the same voice he'd always used on McGonagall. "So childish."
Sirius saw James and Lily a week later, at an Order meeting, but didn't realise the trouble he was in until *they* saw *him*. Lily's eyes narrowed, which he knew was a danger sign, and James grinned, open and friendly, which was even worse.
"Padfoot!" James cried, bounding up and putting an arm around him. "Padfoot, I heard about the birthday present you organised for Harry. I'm sure we'll really appreciate it every time he's formally referred to as the heir to House Overbearing Parents. And you know, Lils and I thought that was so lovely that... you might appreciate the same for your heir."
Sirius blinked, completely uncaring, and then smirked right back. "Couldn't undo what we did, huh?"
James' voice dropped low and dangerous, "...no. So that, Paddy Footy, is why yours are *so* much worse."
Sirius laughed. "Mate, I can't wait to hear them. No, don't tell me - I want to find out when I have kids."
Fifteen years later:
"Sirius!" came a shout from down below.
"You rang?" called Sirius back, jumping the stairs two at a time. He found Harry waiting for him and Moody hobbling away, cackling - madly.
"Sirius," said Harry, two spots of bright red in his cheeks, "Did you know I was the heir to House Poopindor?"
In the next room, Remus' eyes widened from behind his book.
"Or - apparently - the heir to the Noble and Ancient House of Butts?"
"Oops," breathed Remus, and he quietly exited via the Floo.
"How about - and this is how I know it's somehow your fault - the Heir to the Noble and Ancient House of Getting Even With Padfoot?"
Sirius blinked. Twice. Turned his head to the side. Squinted at Harry. "Oh." He started laughing in great, hacking coughs.
"Oh, Harry, I'm so sorry. I forgot..."
Sirius laughed so hard that he had to support himself on the bannister, white stars blooming behind his eyes as he fought for breath.
"Take that, James! Harry, I forgot about his curse and made you my heir!"