The funniest "early family reunion" on the Death Star / crack canon divergence AU that I can think of right now is Darth Vader and C-3PO. Threepio gets separated from the others somehow and ends up running into Darth Vader in some random hallway, and it's just a real "What." moment for Darth Vader. (Threepio is screaming in terror and begging for his life, of course.)
Because, like, that's the droid that HE built for his mom. That's the droid that followed his wife around during the Clone Wars. What the fuck is Threepio doing HERE??? NOW??? Did Obi-Wan (Vader has still caught the Kenobi vibes on the station here, obviously) have Threepio for the past NINETEEN years? That asshole. That sounds SO annoying, too. Good. Obi-Wan deserves that.
Thankfully, this is not as catastrophic as Vader getting R2-D2, because Threepio has had a memory wipe and no one ever tells Threepio much of anything (he's got some information on the Rebellion but most of it is outdated, especially after the destruction of Alderaan). But Threepio has spent the past two days or so hanging out with Luke Skywalker, and also witnessed the destruction of the Lars farm, both of which as revelations may cause Vader to flip out in weird ways. (Artoo is STILL around too??? That traitor.) Possibly, this may be enough of a distraction to allow Obi-Wan to actually slip away and live, but maybe not.
The important thing is that Threepio is taken off the Death Star somehow, so he can become "Death Vader's gaudy gold-plated protocol droid who has anxiety and is annoying as hell but Vader takes him EVERYWHERE". Imperial soldiers from random troopers up to genuinely important Admirals occasionally have to deal with "droid-sitting" duty while Vader is out doing scary, evil Force of Nature stuff and they all hate it, because Threepio never shuts up, has a knack for wandering off (he's trying to pull a daring escape) and nearly getting himself torn to pieces (people have actually gotten hurt trying to follow him), and most people don't have the guts to just turn Darth fucking Vader's pet droid off for a little while. Vader COULD just reprogram him or put in a restraining bolt or take Threepio's legs off, but he can just pick Threepio up with the Force, so it's whatever to him. (There IS a tracker installed, but Threepio doesn't actually know where to run anyway.)
Threepio's official role is "translator" for Darth Vader, which Threepio has somehow taken to also mean "mediator". So, whenever an Imperial officer is getting threatened by Vader, there's a stuffy protocol droid behind him saying things like, "Oh my! I'd listen to him if I were you! What happened to the last fellow was rather unpleasant," and, "It's impossible to get good help these days, isn't it, Master Vader?" and it sucks. The only one who could really do anything to stop this is the Emperor and Darth Sidious couldn't care less about his apprentice's latest purse dog droid.
Unclear whether or not Vader at this point actually has any real fondness for this piece of his past / reminder or his lost loved ones, is just super lonely, secretly thinks Threepio's surprisingly deadly antics are funny, or is using Threepio as bait for R2-D2 (come get him, you little fucker) and the others. Might be a combination of all these things.

















