Not exactly a whole campaign idea this time, but certainly something that could fill several sessions of a Mist Cloak and Vibro-Dagger style game.
Fading Suns: The Urther
No, no, don’t explain it to me. Part of hiring a Scraver information broker is that I don’t ask you why you need an untraceable, concealable, long-range weapon that can kill a target through an energy shield. I’ll just assume that you’re upstanding folks and there’s some big evil that you can’t take out any other way. Maybe a Sathraist that’s got thralls, or a demon possession, right? Right.
Anyway, you’re in luck. Right here on this very planet of Severus is the answer to your hopes. They call him the Urther. Because he’s from Urth. Real creative, right? It’s apparently a big deal for someone from the holy planet to join the Engineers, much less turn that training to becoming a hitman feared across the Known Worlds. I hear he was bad news during the Emperor Wars, and kept going for a while after that.
But he’s more or less retired now. His last mission went wrong, and he’s been laying low. So all you have to do is find an aging Urthish assassin somewhere on the planet. That’s not entirely sarcasm: he does stand out, and I can give you some leads.
The catch is, he’s paranoid as all hell, and with good reason. The Imperial Guard would love to bring him in for war crimes, a bunch of Muster have been trying to get him since the last job, and the Jakovians want to take him out to make sure he doesn’t let slip any Decados house secrets. If you come straight up to him, you’re likely to get shot by one of the best assassins in history.
But it’s not hopeless. He loves nature, so he doesn’t always stay cooped up in his bolt hole. He’s too much of a romantic and has a thing for the ladies, which is part of why his last mission went so bad. Plus, he loves a challenge, so if you can give him something interesting to make, he might be willing to deal.
So, to sum up… wish I could just get you hooked up with your weapon, but for what you want, there’s really only one choice. He’s the best mechanic of death I know of. Good luck.