Because of how it was worded, part of the previous prompt (dark!Han works for Vader) gave me the idea that Han was jealous of Luke and worried he was going to replace him as Vader's favorite. Which in turn made me think of Han being Vader's son.
I could see this working very well with canon. Maybe Vader was extremely depressed after being told his wife and unborn child were dead, so when he finds an young orphan boy he adopts him to soothe the ache. He's surprisingly a good father, and raises Han to be a be value life and hate slavery. So when Han comes across a mistreated wookie slave he saves him even if it means he has to run away from the Empire and his foster dad. Then he starts a life with Chewie as smugglers, and proceed to ANH. If any events from ROTJ are included (ie. Han's torture), maybe Han joining the Rebels was the last straw needed to turn Vader completely evil.
Or things could deviate shortly into ANH if Vader finds out Han is on board the death star. Maybe Vader's like "what are you doing with my son, Kenobi!" and Obi-Wan's says "you know about Luke?" and then Vader's surprised and wanting to know what Obi-Wan's talking about and Obi-Wan is upset with himself for spilling the beans. Maybe this could be a 'Vader joins the Rebels' story if Obi-Wan gets to explain to Vader what really happened.
Or, a complete AU is fine too, these are just some ideas to work with.
Vader adopts Han
I could see this working very well with canon. Maybe Vader was extremely depressed after being told his wife and unborn child were dead, so when he finds an young orphan boy he adopts him to soothe the ache. He's surprisingly a good father, and raises Han to be a be value life and hate slavery. So when Han comes across a mistreated wookie slave he saves him even if it means he has to run away from the Empire and his foster dad. Then he starts a life with Chewie as smugglers, and proceed to ANH. If any events from ROTJ are included (ie. Han's torture), maybe Han joining the Rebels was the last straw needed to turn Vader completely evil.
Or things could deviate shortly into ANH if Vader finds out Han is on board the death star. Maybe Vader's like "what are you doing with my son, Kenobi!" and Obi-Wan's says "you know about Luke?" and then Vader's surprised and wanting to know what Obi-Wan's talking about and Obi-Wan is upset with himself for spilling the beans. Maybe this could be a 'Vader joins the Rebels' story if Obi-Wan gets to explain to Vader what really happened.
Or, a complete AU is fine too, these are just some ideas to work with.