Checked the wiki to see if I remembered things right.
I did and the writing really is this bad.
The Diamond Authority is an evil group of 4 big gems that made all the other gems evil.
They made their race a strict racial caste system where the big buff women must be thuggish guards, the future-seeing rare gems must be pro future seers, the thin dainty girls must be pretty maids, and anyone who's deformed or bad at being their species is a defect to be killed.
Race-mixing aka "Fusing" outside your species results in a bigger stronger creature who's a metaphor for your relationship and its own person. Sometimes. Bad writing. Anyway, "Fusing" inside your species just gives you a bigger version of your species, aka more of the same.
They also colonized and drained planets dry, using a sci-fi thing to consume all life on planets to create more Gems. That's where they come from, don't ask whether Gems were designed by someone else or if they evolved somehow because they never answer these questions they set up as mysteries early on.
Homeworld used to be nice, before the diamonds took over.
Lapis Lazuli the OP Waterbender went from Homeworld to earth when the rebellion had already started.
She got punched in the back-gem and cracked by Bismuth, who sealed this cracked Lapis inside a mirror and hid her in Pearl's room for no apparent reason.
When she was rescued by Steven, the first thing she wanted to do was try to get home. Steven healed her and she flew home.
Then got captured and interrogated. Then taken back to earth by the baddies because she has to be there so she can accept fusion sex with Jasper then begin the undersea torture of the Nappa knockoff bitch any other character could have beaten up solo. Neither of these characters ever matter. Lapis "turns good" and fucks off to a lesbian barn with Peridot to do nothing for 200 episodes. Then all her character development is rushed in her one episode during Steven Universe Future, the show's last-minute "Oh fuck we were cancelled due to bad ratings. Time to get one last season and rush through everything we had planned!" moment.
Anyway 100 out of 300 episodes into the show, we finally find out Bismuth exists I guess.
A psycho gem-hating black lesbian fatty with rainbow dreadlocks.
She'd been locked in a small box by Rose Quartz for saying "Instead of stabbing the light bodies of Gems, letting them regenerate later, lets fucking smash the gem rocks and kill them for real with these pneumatic gauntlets I made!"
See, Pink Diamond (the pussy of the 4 Diamond Authority members) decided to fake her own death and shapeshift into "Rose Quartz", fake leader of the Crystal Gem Rebellion. This caused immeasurable loss of real life and gem life, all because she thought life was pretty and shouldn't be consumed to create more gems. Instead of talking things out with her fellow diamonds or killing them and taking over, she chose this route so there could be a show about this.
Pink Diamond as Rose Quartz then went to earth, fucked a human named Greg, had a child, and died while transferring her gem to this kid.
Saddling him with all of her responsibilities and sins.
When Steven says "Killing your enemies is wrong"
Bismuth says "It is you! You're Rose Quartz, aren't you? I'll kill you!"
then they fight and Steven wins and Bismuth gets put back in the box until the writers decide it's time to hastily forgive everyone.
Why the fuck did I write all of this faggotry?
I hate this show.
60+ episodes of filler human slice-of-life bullshit with unfunny unimportant meme characters wastes time until the next Big Moment that gets built up to for a season then resolved in an afternoon through sheer fucking luck and preachy broken morals. Then the next "reason to stick around for 50 episodes" is established. 50 filler episodes later, the conflict the show built up to gets resolved quickly and a question is given an unsatisfying answer.
Like that time Steven's own human father gets kidnapped by Blue Diamond.
So the heroes go to Blue Diamond's spaceship, waste an episode on making silly faces as they fly to the spaceship (this autism is actually in the show), try to get him back, fail, and then conveniently every single soldier on the Blue Diamond base is of Amethyst's (the fat purple one) race so they betray their ruler by letting these humans and enemy gems escape with Steven's dad, the end. Everyone goes back to the earth and the status quo is resolved.