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Star vs the Forces of the Multiverse

Summary:

In the present day, Star Butterfly and her boyfriend, Marco Diaz, now 23 and 22, discover that magic has returned to their world—but the mystery of how remains unsolved. While Marco is eager to settle down, Star feels a pull towards uncovering the truth behind the magic's resurgence. Her search leads her to Gravity Falls, where she meets Dipper and Mabel Pines, now 25. Along the way, Star and Marco also cross paths with familiar heroes: Sasha Waybright, Anne Boonchuy, and Marcy Wu, now 24, as well as Luz Noceda, her girlfriend Amity Blight, and their friends from the Boiling Isles. Together, this new team must face a powerful shapeshifting threat that endangers their world and the magic within it.

Notes:

Crossover fanfic to cure me of my writing block <3

Chapter 1: Morning in UniEarth

Chapter Text

Sunlight streamed through the window, catching on the bright curtains and filling the room with warmth. A cheesy pop song blared from the sun-shaped radio alarm clock on the bedside table of Star Butterfly and her boyfriend, Marco Diaz. Star was sound asleep, face buried in her pillow, while Marco quietly slipped out of bed. He hit the snooze button, then drew the blinds to soften the light.

He headed into the small bathroom, which doubled as a closet, and stayed there for a while. Star stirred awake just as Marco emerged, freshly shaved, his dark stubble giving him a striking resemblance to his father. Dressed in a simple white t-shirt and jeans, he smiled warmly at Star. She returned the smile, her face lighting up.

“Morning, Star,” Marco greeted her, leaning down to give her a gentle kiss. Star, ever the passionate one, kissed him back with joyful enthusiasm.

“I’m guessing you remembered what today is,” Marco teased, watching as Star nodded with excitement and twirled her way into the bathroom.

Today marked the 10th anniversary of the day they met—when Star first arrived on Earth from Mewni. As she got ready, her mind drifted back over the years, replaying the memories of their journey together. How Marco had become her best friend and, eventually, the love of her life.

But not all memories were pleasant. She thought about her parents, Moon and River Butterfly, and winced slightly. While her relationship with her father was mostly intact, things with her mother had never fully recovered after the final battle for Mewni. Star had been fighting for what she believed was right—restoring the land to the monsters it was stolen from and giving Eclipsa her rightful throne. But Moon had chosen to stand with the Mewman population, even at the cost of bloodshed. Since then, Moon had felt like a stranger. It didn’t help that, four years ago, Moon and River had a second child—a son named Cosmo. Star had only met her brother a couple of times, but she couldn’t shake the uneasy feeling that he was a replacement, a reminder of the rift her mother couldn't mend.

As Star brushed her hair, she thought about how much she missed magic. She had sacrificed it for the greater good—taking it away from everyone, including herself. Being fully human had been an adjustment, even after five years. Since Earth and Mewni merged into what people now called 'UniEarth,' society had changed. Humans grew accustomed to magical creatures, demons, and monsters. Most monsters chose not to live in cities due to their size, but those who did still faced prejudice. It seemed that even in this new world, racism persisted.

On the political front, Eclipsa now served as President of the United States, with her daughter Meteora, now six, and her husband Globgor by her side. Star, as Eclipsa’s unofficial niece, often enjoyed special perks from her close connection to the President.

Life had moved forward for others too. Tom Lucitor and Janna Ordonia were engaged, with Janna hosting a popular ghost-hunting show while Tom served as her cameraman. Together, they traveled the world visiting haunted locations, with Tom relishing the chance to scare ghosts rather than vice versa.

Ponyhead had become a TikTok star with millions of followers, but her busy schedule meant she barely had time for Star anymore.

And then there was Kelly. Star had always felt a little conflicted about her. Kelly had briefly dated Marco but never quite got over him. When she found out Star and Marco were together, she left their friend group, leaving behind a bittersweet memory.

Star stared blankly at the wall, her mind drifting as a familiar wave of restlessness set in. At 23, she found herself unemployed, though it wasn’t as though she needed to work. After all, she and Marco had essentially reshaped the world with their love, and Eclipsa kept them provided. Still, sometimes it felt like they had both peaked at 15, back when everything was about adventure and magic.

Marco had found his footing, at least. He never lost his passion for karate and had recently taken over as dojo master at the Echo Creek mall. It was a small start, but Marco had big plans—first the dojo, then something even greater.

Star, on the other hand, struggled to find her place. She’d tried countless hobbies, each one ending in frustration. Her ADHD made it hard to stick to any one thing, leaving her with more half-finished projects than actual accomplishments. She missed magic most of all. Without it, nothing seemed to fit. She’d even tried learning sleight-of-hand tricks and stage magic, but none of it gave her the spark she craved.

The absence of real magic left a void that nothing else could fill.

As Star sat at her vanity, her thoughts running in circles, Marco walked into the bathroom, his attention focused on his phone. He barely glanced up, his fingers swiping through a series of notifications.

“Okay, so the Bud Barn opens at—oh, wait, it's already open,” Marco said, eyebrows raising slightly as he scanned the screen. “We can swing by there first, then lunch at Britta’s Tacos. And after that... what do you want to do?”

Star shifted her gaze from the mirror to Marco, the corners of her lips curving up into a soft smile. She stood up, brushing her hair behind her ears, and crossed the room to him. Without a word, she leaned in and kissed him lightly on the lips, a small spark of warmth blooming between them.

Marco blinked, caught off guard by the sudden affection but quickly sinking into the kiss, his hand resting on her waist. When she pulled back, her eyes were bright and playful. “Maybe a movie?” she suggested, her voice carrying a hint of excitement.

Marco grinned, sliding his phone into his pocket as he met her gaze. “Sounds like a plan. Anything in particular? Or do I get to pick this time?” His tone was teasing, knowing full well that Star often insisted on the weirdest, most chaotic movies possible—usually ones with talking animals, explosions, or both.

Star chuckled, playfully nudging him in the ribs. “Maybe I’ll let you pick… just as long as it’s not something boring.”

Marco laughed, shaking his head. “No promises. You’re talking to the guy who loves karate documentaries.”

Star rolled her eyes with an exaggerated sigh but smiled all the same. “Fine, but if you pick something about karate, I’m picking the snacks.”

“Deal,” Marco replied, stepping closer to wrap his arms around her. He looked down at her with that familiar, tender expression she loved so much. “You ready for today, Star?”

She paused for a moment, resting her head on his chest as she thought about their day ahead. It was normal, almost mundane—trips to shops, lunch, maybe a movie—but that wasn’t necessarily a bad thing. In fact, there was something comforting about it. With Marco, even the most ordinary days felt special.

“Yeah,” Star said softly, looking up at him. “I’m ready.”

With one last kiss, the two of them headed out, ready to face whatever the day—and the world—had in store for them.