For the meme: The skywalker twins
Headcanon A: what I think realistically
They never really have a conversation about Anakin Skywalker. They try, a few times, but it devolves into Leia shouting or Luke getting angry—angry in that black, festering way he has, when Leia can feel it in the air, choking as smoke from a chemical fire. He makes her cry once, even though she tries to hide it from him, and it’s the worst thing either of them has ever done to the other. (They’ve hated one another sometimes, but neither of them has ever hurt the other. Not once.) They do try to talk about it—this, more than anything else, the blood that unites them—until it’s too horrible to keep trying, so they stop.
Headcanon B: what I think is fucking hilarious
There was a solid eighteen standard days on Hoth when Luke and Leia turned the entire base into a madhouse—it might have been longer, but Mon Mothma intervened and sent them on missions at opposite ends of the galaxy. This is still known colloquially as “The Great Prank War of Echo Base”, and whenever it’s mentioned, Han looks haunted.
“Listen,” he tells Ben once, very seriously. “If you ever have to pick sides between your mom and your Uncle Luke…the only correct answer is to run really fast in the opposite direction.”
Headcanon C: what is heart-crushing and awful but fun to inflict on friends
They only tell a handful of people about the fact that they’re brother and sister. Luke has spent the last five years telling anyone who would listen that he’s Anakin Skywalker’s son, and since Cloud City has been—almost—as open about the fact that Darth Vader is Anakin Skywalker, to the point that it’s not much of a secret that Luke Skywalker is Darth Vader’s son. (It serves to make him even more of a figure of myth, even among the Rebellion. Darth Vader’s son, the Jedi, who is going to kill his father and win the war.)
On the other hand, while most of the rebels who knew Bail are aware that Leia was adopted, Bail and Breha always insisted she was just an orphan of the Clone Wars, and honestly, what are the chances that Darth Vader had two secret children? (Yeah, right. This is real life, not some daytime holodrama.) Leia wants nothing to do with her biological origins, anyway; she’s happy to let Luke be the object of whispers and worship, to be tinged with the fear of those who don’t know him.
Still, sometimes Han has to nudge Leia, pull her away from Luke, because what is affectionate between brother and sister looks dangerously like infidelity in any other context.
Sometimes Wedge gives Luke pitying glances, because Leia and Han are whispering to one another, smiling the sort of smile lovers are entitled to, and Luke wants to protest, no no stop, let me have this complicated uncomplicated thing, for myself.
Sometimes Leia gets asked what her relationship to ‘Skywalker’ is. In all the intervening years, Leia has perfected an empty smile, to say warmly, “Luke is one of my oldest friends.” Sometimes, if she’s feeling vicious and/or guilty, she adds, “I consider him almost a brother.”
Headcanon D: what would never work with canon but the canon is shit so I believe it anyway
Being children of the Living Force is stranger than you might imagine, an embodied a war between your humanity and the weight of the galaxy. Leia sometimes wakes up inside Luke’s skin—just for half a second, her eyesight sharper and the world written in neon light because oh, that’s the Force, that’s what it means—before she’s slammed into her own body again. Luke has dreams of Aldera, where he walks along broad avenues and up into the mountains and every person he meets is on fire, burning up to ash, but he still must carry them, all the same.
Leia cries once for no reason, standing in the middle of a Senate session—so hard she has to excuse herself, and she screams her grief in the refresher, collapsing to her knees. (Luke is on Tatooine, standing over the ashes of his homestead.)
Luke jolts awake in the middle of a pile of rubble and bodies and feels all the blood drain from his face because he doesn’t know if this was him, or if this is something he can never, ever ask Leia.
(Neither of them die. This is not their inheritance as the Living Force, but what they inherited matrilineally. Surviving—that’s something human.)