@tnott said “So the expert on all of this is… you?” (for Sirius from Theo)
"Yep." Sirius spread his arms out in mock celebration. "Welcome to the Headquarters of Magical Objects, and the answers to all the burning questions of your heart's content, granted that it's stored in that filing cabinet there, and relates to something no one in all the ministry actually gives a damn about." He gestured to a nearby cabinet so dusty, it was clear no one had cared to open it in years.
Two decades ago, Sirius would have considered himself the goddamn expert of the whole fucking universe. Yes, he'd been a cocky prick, but he'd had good reason for it--he'd been good, damn good. He and James hadn't just been popular in the social scene alone; they'd been top of their class. Sirius had gotten top grades in all of his OWLs and NEWTS without trying, and he'd managed to become an animagus when he was only fifteen years old, when many grown wizards couldn't pull it off. So yes, once upon a time, Sirius Orion Black had been full of promise, a rising star in the wizarding world.
And then came the war. And prison. And another god damned war. He was twenty-two when he was locked up, thirty-four before he'd managed to escape, and thirty-eight by the time the war was over and his name cleared. By that age, most people had at least some idea what they'd been put on this earth to do, but Sirius had spent the last year or so shuffling around from one job to the next in the Ministry. They had all been easy enough to get; the Ministry owed him a debt, after all. Twelve years of false imprisonment, it turned out, was worth a job or two, so Sirius tried them all, quitting after only a few short weeks.
And that was how he'd come to work in the Misuse of Muggle Artifacts Department. It had been a good enough excuse to get paid for taking apart the things he already cared about: like his motorcycle, or Arthur's car. He'd long been interested in muggle technology--in muggle anything, really, that might have pissed off his parents. Now, however, they had him digging up old muggle artifacts that had been cursed and placed in museums across the country: old devices from the Roman era and Medieval Europe. Some of it had been cursed long ago with anti-theft charms and the like, but some had some pretty nasty curses, the sort of thing his parents might have concocted, and the sort of thing he'd unearthed in his family home, Number 12 Grimmauld Place, a hundred times over.
So maybe, in a manner of speaking, he was an expert. He slumped back into his office chair--he was still surprised he had an office in the first place--and threw his boots up onto the desk, crossing his arms behind his head. "What can I do you for?"