It all started with Steven Universe having used the Hourglass from "Steven and the Stevens" just to form a band. One Steven accidentally warped back to the Rebellion and caused it to ruin. It was at one of the first battles at the Ancient Sky Arena where during the war, Steven appeared out of nowhere in front of a giant Homeworld Garnet fusion, distracting Rose Quartz from her battle. The fusion was about to kill him, but Rose jumped in the way of the attack as she couldn't let an innocent human civilian die in enemy crossfire, dissipating her form in the process. Thankfully, Steven quickly warped back to the present, and destroying the Hourglass causes the timeline to merge with the main one. But Black Rose, using her newfound powers caused by the loss of the rebellion, the Earth, and her subsequent imprisonment, became immune to the time change, making her the sole survivor of the timeline. Unaware that the Earth of this reality is still alive, Black Rose traveled to Pink Diamond's Garden where she found Spinel still waiting for her three years prior to the Movie. Together, they gather up the rejuvenator and the injectors filled with the collected Diamonds' essences and Rose's tears to liberate Homeworld's colonies as revenge for Rose's imprisonment, starting with Earth.

At the Lighthouse Hill, Steven and the Crystal Gems lay on the grass and relax.

Steven: I want everything to stay exactly like this and never change.

Garnet: (sits up in alarm) No...

Steven: (confused) Huh? Garnet, what-

The Crystal Gems look up at the cloudy sky and spot Black Rose's injector lowering from the clouds. It looms over Beach City and points towards the hill.

Spinel: (riding on top of the injector) (cheerfully) (calls out) HI! I'M SPINEL! IS THIS PLANET EARTH?!

Steven: (confused) Um... yeah?

Spinel: OH! (giggles) (calls out to Black Rose flying above her) Yep! This is the place, alright! Playtime!

Black Rose: (stoically) Perfect. (flies down to the middle of the injector and lets out an enraged scream, activating it)

Garnet: (serious) Move! (the Crystal Gems retreat as the injector drills into the earth)

Amethyst: (annoyed) Hey! Nice park job, dinguses!

Spinel: (jumps down to the middle of the injector next to Black Rose) (happily giggles) Well, well, well, well, WELL! (shapes her eye into a telescope, stretches her other hand into another telescope to Black Rose so she can see too) Let's take a look at the menagerie!

Black Rose: (to Amethyst, perceiving her as Jasper) You must be the little Jasper who ratted Rose out, (to Garnet, perceiving her as Demantoid and Pyrope) you must be the Garnet fusion that tried to attack the human, (to Pearl, perceiving her as White Pearl) and White Diamond's Pearl! (annoyed) (sighs) Of course. They still took you from Pink. (sarcastically) Isn't that just swell? No surprise there.

Pearl: (recognizing Spinel) (shocked) It can't be... Spinel? As in, Pink Diamond's Spinel?

Spinel: (giggles) (playful) But it can be! And it is!

Black Rose: And Pink is gone, you can call me Black Rose. I have a new style, and brand new toys that's going to put an end to this colony, (angry) ONCE AND FOR ALL!

Steven: (nervously) Whoa, this has to be a misunderstanding. In case you haven't heard, the colony has been-

Black Rose: (perceiving Steven as Blue Diamond) (bitterly) Yes, I know, Blue. I had this little message back at the moon base (throws her shield at Steven, knocking him back) ON LOOP!

Spinel: (sarcastically) And I just LOVE the part where Pink Diamond spent the rest of her days (sympathetically) alone in that awful tower until her planet's completely gone! So tragic!

Black Rose: (smiles to Spinel) Thank you, Spinel. At least you were always there for me. (Spinel returns the sentiment) (she and Spinel then jump down the injector to fight the Gems)

Spinel starts by toying with the Gems, dancing in front of Steven. She then dodges Garnet's attacks with ease, flicks Pearl on the nose, and pulls Amethyst's hair down her face. She ends by throwing Pearl to Black Rose.

Spinel

That's right we heard the story,
Over and over again,
Gee, it's swell to finally meet her so-called friends!
That's right, we heard the story,
Don't really like how it ends,
Gee, it's swell to finally meet her so-called friends!

Black Rose then traps Pearl in a bubble and juggles her around before throwing her to the ground, hard. She then sweeps Amethyst off her feet and starts smashing her repeatedly between two shields like a pair of crash cymbals. Finally, she flies to Garnet and spins her around faster and faster until she pops her shield at Garnet, smacking her aside.

Black Rose

What did they say about me?
What did they say?
See what they've done to me?
See what they've done?
Did you go on without me?
What did you do?

Black Rose then rejoins Spinel and she wraps around her body as they both intimidate Steven together.

Spinel and Black Rose

Did you think all this time we wouldn't find out about this?

Black Rose constructs ropes with her powers, lassoing Steven and Garnet while Spinel grabs hold of Amethyst and Pearl and pull them all in, smashing them into each other, while Spinel swings herself and Black Rose up to the lighthouse's roof.

Spinel

Oh, that's right, we heard the story,
Over and over again,
Gee, it's swell to finally meet her so-called friends!

Garnet: They're running circles around us!

Amethyst: (annoyed) I'm rusty! Give me a break!

Pearl: (recognizing Black Rose) (shocked) It really is her. But that's impossible.

Steven: You know her, Pearl? Can you tell us who she is? And Spinel? And why does she look like Mom?

(Black Rose responds by glaring at the gems and clenches her teeth in anger)

Black Rose

Who am I?
Who am I?!
What are you even saying?
I'm the loser of the war you didn't know you were winning!
Let's start another war

Done with toying with the Gems, Spinel summons her scythe and her rejuvenator and activates the latter as she and Black Rose dance together and fuse.

Spinel and Black Rose

This time we get to win!

Spinel

Lives on the line

Black Rose

Winner takes all

Spinel and Black Rose

Ready or not,
Let's begin!

Morganite, the fusion of Black Rose and Spinel, appears sporting a unique physical form: being one head shorter from Blue and Yellow Diamonds' height, Black Rose's pink glowing skin, black marks down her four eyes with Spinel's white sclera and cartoony irises on top of her face with Black Rose's black sclera and pink irises on the bottom, Black Rose's head and body shape, nose, and long messy hair, Spinel's neck, mouth, pigtailed hairstyle, and limbs with two more at the waist without her gloves. In addition, her outfit consists of a dark pink V-neck dress resembling Spinel's top and Black Rose's long skirt shortened with the bottom cut into V-shapes, her waist wrapped in a white trim, and Spinel's shoes colored black and sleeves turned puffy.

Morganite (voiced by: Andrea Libman)

Oh, that's right, I heard the story,
Over and over again,
Gee, it's swell to finally beat her so-called friends!
Oh, that's right, I heard the story,
Don't really like how it ends,
Gee, it's swell to finally beat Pink's so-called,
So-called,
So-called
Friends!

Morganite leaps off the lighthouse, using Spinel's scythes and Black Rose's swords to feint an attack at the Gems until she uses Spinel's stretchy powers to deliver a kick to Steven's face, knocking him back. Twirling her weapons around, she then utilizes Spinel's powers to circle around Garnet, Amethyst, and Pearl while also using Black Rose's powers to trap them in a pink dome, and uses the lighthouse to propel herself towards them and slice apart their physical forms with Spinel's rejuvenator, poofing all three of them.

Steven: (serious) That's enough! (summons his shield)

Morganite: (mockingly) Aw, what's the matter, Blue? Miss your court, already? Well, don't worry. YOU'RE RIGHT BEHIND THEM! (slashes Steven with the rejuvenator)

Steven: (nervously chuckles) That was nothing!

Morganite: (chuckles evilly) Then I guess you don't mind... IF I DO IT AGAIN! (slashes Steven again) AND AGAIN! (slashes Steven two more times while laughing maniacally)

Steven: (seizing the rejuvenator) Cut it out!

Morganite: (annoyed) You don't poof very easily, do you, Blue? Figured as much. (smirks) Just wait! Your Diamond powers won't stand a chance against me nor Black Rose's injector, not after what I did to your gem! And soon, I will put every one of the colonies back to the way it was and there's nothing you or the other Diamonds can do about it.

Steven: (confused) Blue? What are you talking about? I'm not-

Morganite: (serious) Don't try to fool me with that human disguise, Blue. (referring to Steven's blue shirt) Obviously, your color gave you away. And that form looks exactly like the human Rose tried to save at the Sky Arena... (mockingly) that was you, wasn't it? (laughs maniacally and unfuses as Steven pulls the rejuvenator away from her and slices apart Black Rose with it, poofing her)

Spinel: (happy) Well, that was fun! Let's play keep away! (stretches and takes her rejuvenator back from Steven) Yoink! (retreats giggling)

Steven: (confused) Huh? W-Wait! (sighs in frustration) At least I've got one of them. Now to bubble you before anything else happens. (tries to bubble Black Rose, to no avail) (confused) Huh? Where's my bubble? Come on... (tries to bubble Black Rose again, only to fail) (examines his reset gem) What's going on? (examines Black Rose's pink diamond, to his confusion) And this looks like... Mom's gem, but why?