Part of the charm of the original Star Wars (now known as Episode IV: A New Hope) were the characters and how they were written...not so much the special effects, the sound, and all the other things that made the movie seem so fresh "a long time ago" in 1977.
It was the flinty banter of the hayseed hero, the haughty princess, and the ego-bag smuggler. And it was the way the thing was edited to catch every hint of emotion from its players...who'd done maybe one or two films previously. Creator George Lucas had wanted to make a "space opera" along the lines of the old "Flash Gordon" movie serials (in fact, he tried to get the rights to Flash Gordon but was unsuccessful) and that included dialog of the fast-paced variety that reflected the theatrics of serials, rather than, say, the mumblings of Method actors.
The Luke-Leia-Han triangle dynamic was a sub-text among the whooshing and zapping that made up the larger conflicts of the story. Like everything, it got untangled over the trilogy-story of toppling/exploding the Evil Empire. Luke's impetus for joining the struggle (besides his own desire to quit the moisture-farm and become a pilot) was the flickering image of the Princess pleading for help. For Han, it was a hired job to take an old wizard and his farm-kid to the planet Alderaan, which ended up with the planet in rubble and their ship being captured. Han just wanted to get off the Death-Star, but, Luke, learning the Princess was on-board, roped the Corellian pirate and scrumrat into crashing Leia out of detention, and getting her to safety (they didn't really need to—the plans to the Death Star were down-loaded into one of Luke's work-droids, they just didn't know it yet).
Luke wanted to rescue the Princess, but Han and she didn't exactly hit it off right away, bickering like each one was in charge of things. But, Han's character arc was to push him from being a selfish loner (I mean, look at his name!) to a a slightly more noble team-player, so, eventually, the sand-papering scorn and mockery wore down his rough edges. Luke was still beholden to the Princess, so Luke and Han settled into a competitive rivalry over who would get her attention.
UA Cinema 150
It wouldn't be until a third of the last party of the trilogy that Luke would learn why he was drawn to the Princess—Force-siblings?—which would lead to making the ultimate sacrifice of surrendering himself to the Empire. Han and Leia would begin an affectionate relationship when left-alone in the romantic surroundings of a space-slug's belly. And in all the mishegoss of rescuing each other from some threat or another, the two rivals wound up in a mutual mode of getting out of each other's way for the Princess' hand (even if Luke could have used an extra one).
So, it's amusing that, in this round of of the Leia-Han tussle, he keeps calling her "sister". There's no way—NO--WAY—that there's any sort of pre-saging of future events, even if the director says he knew all along (although there's a precedent in The Thief of Bagdad, and Star Wars was "influenced" by a lot of diverse film culture), but George Lucas keeps changing his story...about changing his story.
Still, it's amusing looking at it in retrospective. The scene itself produced a chuckle when I first saw the film the day after its opening day at the late, lamented UA Cinema 150...which went on to play the film...for more than a year.
The Set-up: It is a dark time for the galaxy (blah blah blah). Farm-boy Luke Skywalker (Mark Hamill), inspired by ex-Jedi Knight Obi-wan Kenobi (Alec Guinness) has abandoned his home-planet of Tatooine to save Princess Leia Organa (Carrie Fisher) from The Galactic Empire's new battle-station, The Death Star. Having saved the Princess and lost Kenobi in the attempt, they flee the Death Star aboard the Millenium Falcon, piloted by spice-smuggler Han Solo (Harrison Ford) and his wing-
manwookie Chewbacca (Peter Mayhew).
STAR WARS Episode IV A NEW HOPE
From the JOURNAL OF THE WHILLS
by George Lucas
Revised Fourth Draft January 15, 1976
INT. MILLENNIUM FALCON - COCKPIT
LEIA You needn't worry about your reward. If money is all that you love, then that's what you'll receive!
HAN she's got a lot of spirit.
STAR WARS (Episode IV—A NEW HOPE)
Words by George Lucas
Pictures by Gilbert Taylor and George Lucas
Star Wars: Episode IV—A New Hope is available on DVD (in all sorts of versions) on 20th Century Fox Home Video.