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English
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Published:
2025-08-24
Updated:
2026-03-09
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60,161
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41/?
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Mario & Steven: Dimensions Collide

Summary:

After the destruction and recreation of the universe, Mario's birthday is turned into a holiday known as Super Mario Day. One year, the evil Bowser attacks once again, and this time he has a horrifying new power: the ability to travel to other universes entirely separate from his and Mario’s own. Mario pursues Bowser into one of his portals and ends up in a mysterious new universe, where he meets and befriends a half-human, half-alien boy named Steven, who also happens to be a universe savior celebrating his birthday. Things unfortunately only get worse for both boys, as they soon find out that Bowser and an old friend of Steven’s have joined forces to fulfill an ancient grudge and conquer all the dimensions of the multiverse. Will Mario and Steven have what it takes to defeat this alliance, or will all existences be plunged into eternal darkness by two vengeful souls?

Notes:

Finally achieving maximum autism by writing my pipe dream crossover lol! Mario and SU both mean everything to me and I don’t think I’d be the person I am today without them, so think of this as my love letter to them. This is my first-ever fanfic so I apologize in advance for any sloppy writing + irregular uploading. Nonetheless, thank you so much for reading and I hope you enjoy this silly little passion project of mine. :)

(And thank you to Shigeru Miyamoto and Rebecca Sugar for changing my life <3 All rights go to them and their respective teams and companies)

Chapter 1: Happy Birthday, Mario!

Summary:

Mario and his friends get together to celebrate Super Mario Day, but little do they know that they’ll all be getting a surprise.

Notes:

(See the end of the chapter for notes.)

Chapter Text

Once upon a time, there existed the Mushroom Kingdom, a bustling and prosperous land inhabited by the mushroom-like Toads and ruled by the human Princess Peach. One night, as the kingdom was celebrating the centennial Star Festival, it was invaded by Bowser, the evil and ferocious Koopa King. He ripped Peach’s castle straight out of the ground and carried it and its owner off to the center of the universe, where he created a galaxy to rule the cosmos from. He also stole a series of seven powerful artifacts known as the Grand Stars, which he used to power the various parts of his galactic empire and increase his own strength. Bowser’s ferociousness knew no bounds, and it didn’t take long for much of the cosmos to be devastated by his might.

But then, just as all hope seemed lost, a hero rose up: Mario, a humble yet powerful young human who was a longtime friend of Peach’s and a longtime enemy of Bowser’s. He’d fought the Koopa King countless times before, and he knew that only he could stop him. With the help of the mysterious space guardian Rosalina and her children, the Lumas, Mario took back 6 of the 7 Grand Stars and used their power to travel to the center of the universe, where he and Bowser finally had their great clash. Both sides fought long and hard, but in the end, Mario emerged victorious, claiming the final Grand Star.

With all seven Grand Stars out of Bowser’s grasp, his empire began to collapse, taking the entire universe down with it via a supermassive black hole. To stop the destruction, the Lumas sacrificed themselves, diving straight into the black hole to trigger a massive supernova that resulted in the universe being destroyed and recreated. Bowser was defeated, peace was restored to the universe, and Mario’s birthday was made into a new holiday known as Super Mario Day, made to honor him and his heroic deed.

* * * * *

“Wow, Bro, your biography turned out great!” Luigi exclaimed as he closed the book titled The Tale of Mario , a biography of his eponymous older brother written by Princess Peach. 

“It sure did!” Mario agreed. “Best birthday present ever! Peach did a fantastic job. I can’t wait to see what the rest of the kingdom thinks of it!”

Suddenly, a knock came from the front door of the Mario Bros. house. “I’ll get it,” Mario said as he stood up from the couch.

He walked over to the door and opened it to find a purple Toad with a messenger bag slung over his shoulder. It was Mailtoad, the Mushroom Kingdom’s mailman.

“Happy Super Mario Day, Mario!” Mailtoad greeted as he took out a pink envelope from his bag. “To Mario” was written on the front in red ink, and the envelope was sealed with a heart-shaped red wax seal. “Princess Peach sent me to deliver this letter. Sounds like she has a special surprise planned for your birthday."

“Thank you, Mailtoad,” Mario replied as he took the letter. “I’ll read it right away.”

“Great, ‘cause that’s what Peach told me to tell you! Have a happy birthday!”

Mario waved goodbye to Mailtoad as the latter walked off. Mario then closed the door, sat back down on the couch, and opened the envelope. The letter inside read:

Dear Mario,

Happy Super Mario Day! I hope you like your biography.

I hear the sky is going to be beautiful tonight. Would you and Luigi like to meet me, Yoshi, and Toad at the castle to stargaze while we all share some cake?

-Princess Peach

A big grin spread on Mario’s before he shot up from the couch. “Ooh, someone’s excited,” Luigi remarked.

“Peach has invited us to hang out at the castle with her and Toad and Yoshi!” Mario exclaimed. “Let’s not waste any time! Let’s-a go!”

Mario ran out the door just as Luigi stood up from the couch. As he began to follow his brother, Luigi shook his head and said to himself, “He sure loves his princess. And her cake.”

* * * * *

The Mushroom Kingdom was more than prepared for the year’s annual celebration of Super Mario Day. Banners displaying various Mario-praising phrases such as “HAPPY BIRTHDAY MARIO” and “HAPPY SUPER MARIO DAY” hung from all the various street poles of the kingdom’s capital city Toad Town. The gray stone statue of Mario in the center of the town square had been decorated with lights to match his actual colors, and a fireworks display of various images of Mario lit up the sky. Several of the town’s eponymous residents had their faces buried in their own copies of The Tale of Mario.

Just as night fell and a beautiful host of stars joined the fireworks in lighting up the sky, Mario and Luigi began walking through the Toad Town streets on their way to Peach’s castle. As they did, Toads shouted various praises at Mario: “Happy Super Mario Day, Mario!” “Thanks for all you’ve done for us, Mario!” “Enjoy your special day, Mario!” “I’m lovin’ your biography, Mario!”

“Thank you, everyone!” Mario shouted as he and Luigi reached the castle gates. Captain Toad, the leader of the Toad Brigade, stood guard to the Bros.’ left, while a yellow Toad Brigade member slept to their right.

“Evening, Mario Bros.!” Captain Toad greeted as Mario and Luigi approached. “Happy Super Mario Day!”

“Thank you and evening to you too, Captain,” Mario replied. “Is Peach available?”

“Yep! She and Yoshi and Toad are waiting for you up on the castle balcony. Lemme just open the gates for you.”

Captain Toad used his foot to press a hidden red button on the ground behind him, and the gates slowly opened up the way into the castle courtyard.

“Off you go!” the captain said. “Say hi to Peach for me!”

“Will do!” the Bros. shouted as they raced towards the castle. 

Sure enough, Princess Peach stood on the castle’s balcony, in front of a three-tiered cake decorated with images of stars and mushrooms on the sides and a cake topper in Mario’s likeness. Next to her was her trusty sidekick Toad and Mario’s dinosaur friend Yoshi. 

The trio noticed the Bros. and waved to them. “Hi, Mario Bros.!” Peach greeted. “So glad you made it! The cake’s all ready! I set up a nice stargazing spot in the yard, too!”

“Great!” Mario exclaimed. “We can’t wait!”

* * * * *

Suddenly, just as the Bros. reached the doors leading into the castle, a loud, terrifying roar echoed through the area. It was a sound everyone in the Mushroom Kingdom knew all too well: the roar of Bowser, King of the Koopas.

Sure enough, a fleet of Bowser’s airships came flying in from all directions, shooting meteors and Bullet Bills and Bob-ombs and all sorts of other explosives from their cannons. A black flag emblazoned with Bowser’s insignia - a red silhouette of his face - flew from a flagpole on each ship. Terrified Toads fled the streets, screaming and tripping over each other as they scrambled to avoid the projectiles. 

“IT’S BOWSER!” one Toad screamed.

“RUN FOR YOUR LIFE!” cried another.

The Super Mario Day banners burned to ashes, the fireworks display ceased, and a single giant meteor reduced the town square Mario statue to smithereens. Before long, all of Toad Town was on fire, houses collapsing and smoke filling the air. It looked exactly like Bowser’s attack during the Star Festival: complete and utter fiery chaos.

Then, a massive airship - over twice as big as any of Bowser’s other airships - flew in from the skies behind the castle and stopped directly above it. And standing aboard was, you guessed it, Bowser. He had the same menacing appearance as he always did - tall and bulky reptilian build, spiky turtle shell, draconic head - along with one small new detail: a familiar-looking indigo orb surrounding a black star, seemingly embedded in his chest.

“Gwahahahaha!” the Koopa King laughed. “Super Mario Day, huh? And I wasn’t invited? Typical!”

“You’re not welcome at any party of ours, Bowser!” Mario retaliated. “Or anytime at all, for that matter! Now take your little fleet and get lost!”

“Hahaha! You wish, plumberboy!”

Bowser leapt off his airship and onto the castle balcony - directly on top of Peach’s cake, reducing it to a smushed pile of pastry and frosting. Toad and Yoshi held up their fists, ready to fight, but Bowser knocked them both off the roof with two simultaneous uppercuts. Peach screamed and tried to jump off the balcony into Mario’s arms, but Bowser snatched her straight out of the air and jumped back onto his ship.

“Hey!” Mario, Luigi, Toad, and Yoshi all shouted.

“Mario!” Peach cried, trying in vain to escape Bowser’s grasp. 

Suddenly, a giant UFO appeared above Bowser’s airship - the same UFO he’d used to steal Peach’s castle during the Star Festival. Sure enough, it used its three lasers to draw a circle around the castle, and four of Bowser’s smaller airships grabbed onto the castle with huge chains and pulled it out of the ground.

“Hahahahaha!” Bowser laughed. “The party’s over, Mushroom Kingdom! For I have gained a new power: the ability to travel to other dimensions! With it, nowhere in the multiverse will be safe from the might of the Koopas, and we shall finally get our millennia-in-the-making revenge on those traitorous Diamonds!”

“Diamonds?” Mario asked. “Who are-”

Before Mario could finish, Bowser raised his hands high above his head, and the star in his chest gained red eyes and glowed with black light. A large black magic orb formed in his hands, which he threw in front of him to create a massive portal that resembled a black hole.

“Follow me, troops!” Bowser commanded his other ships as his personal ship entered the portal. “Princess Peach is ours once more, and now the Diamonds shall be next!”

The airships stopped their attack and followed Bowser’s airship into the portal, Peach’s castle in tow. Just as Bowser disappeared into the portal, he looked at Mario, grinned wickedly, and said, “Happy birthday, Mario. Catch me if you can.”

“Wait!” Mario shouted as he sprinted towards the portal, ignoring Toads’ cries for help. “Woah, Bro! Wait!” Luigi shouted after him. “What are you-”

Toad kicked him in the leg and shouted, “What do you think? Going after Peach, obviously! We can’t just let Bowser take her! C’mon, Yoshi!”

“Yoshi!” Let’s go! Yoshi exclaimed.

Luigi sighed. “Oh, mamma mia…”

He and Toad climbed onto Yoshi’s back, who then sprinted after Mario. With the highest leaps they could muster, Mario and Yoshi dove into Bowser’s portal just as it shrank away and disappeared, leaving behind the burned remains of Toad Town.

* * * * *

When Team Mario entered the portal, they found themselves flying through what looked like some sort of strange purple tunnel, like a rift in the fabric of space-time. Bowser’s fleet flew directly in front of them.

“You’re - not - getting - away - that - easily, Bowser!” Mario yelled as he and Yoshi tried to push themselves closer to Peach’s castle. Just as they got within a stone’s throw of it, Bowser’s advisor and adoptive father, Kamek the Magikoopa, suddenly appeared in front of them.

“Kekekekeke!” Kamek laughed as he raised his magic wand, about to cast a spell. “Sorry, boys, but you’re not invited to our party! Have a safe flight!”

With a loud laughing scream, Kamek cast a magic blast at Team Mario, knocking them all far away from each other - and out of the portal tunnel. They all screamed in terror as they disappeared.

“Nooooooooo!” Peach cried as her only hope vanished before her eyes.

Notes:

As stated in the tags, there’ll be multiple POVs in this story. Some chapters will focus on our protags and/or someone on their side, while others will focus on our antags and/or someone on their side. For the first few chapters the story will just be about setting up the conflict and establishing who all our protags and antags are, so there probably won’t be much, if any, POV switching for a while. Fingers crossed that it won’t be too convoluted lol.