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English
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Part 4 of my Percy Jackson crossovers
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Fandom Trumps Hate
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Published:
2025-09-22
Completed:
2025-11-18
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8/8
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Thunder of Hooves, Flash of Speed

Summary:

In which speedsters can create wormholes between worlds and Hazel Levesque rides the fastest horse on earth.
In which Barry meets another speedster and chases after criminals, Cisco isn't allowed to run all the experiments he wants but still gets more than he bargained for, and Caitlyn makes a friend.

OR

The Riodanverse x The Flash crossover someone did, in fact, ask for.

Notes:

Happy Tuesday.
I participated in the Fandom Trumps Hate (FTH) event this year, this is the first of two fics I wrote because of it.
Thank you to BookKeep for bidding and donating. This was a very fun idea and I greatly enjoyed writing this fic - hope you'll enjoy reding it.
Have fun.

(See the end of the work for more notes.)

Chapter 1: Travellers

Summary:

Tuesday.

Notes:

(See the end of the chapter for notes.)

Chapter Text

Barry Allen is the fastest man alive. Which means that he usually isn’t too slow.

Too late, sure, that’s something he’s on the regular, ask anyone he works with or interacts with socially from time to time. But too slow usually isn’t a problem for him.

That’s why it’s particularly frustrating when he arrives at the scene of a violent robbery only to find the offending party already gone. All that’s left from the attack are scared bystanders, injured bank-employees and an odd crackling in the air.

“They’re gone,” Barry informs Cisco and Caitlyn via his headset. “I’m heading back.”

He doesn’t bother staying behind as the Flash. He knows he’ll be called in to investigate this crime scene once he’s on shift at the station in not even an hour. He needs to talk to Cisco and Caitlyn before that, take a shower, get dressed.

His friends are waiting for him at Star Labs when he returns to their headquarters, sympathetic looks on their faces.

“That was the third time in two weeks,” Barry says once he’s changed into civilian clothes and has a protein bar in his hands. He settles onto one of the comfy office chairs they have in the lab that has become their main staging area for missions. He knows he’ll have to head off soon, but takes the comfort for a few minutes, nonetheless. “Please tell me we’ve got a way to track them.”

Cisco had dubbed the group the Portal Posse. Not his best work, but descriptive enough.

Caitlyn still has that sympathetic smile on her face, the one that says “I get that you’re upset, and rightfully so, but it’s going to get better”. She’s been looking at him like this a lot, those past two weeks. Ever since a team of robbers with some kind of teleportation technology showed up in Central City.

Their MO is consistent and easy enough: They get into a bank, or a museum, or a jewellery store and under great force make the employees hand over their valuables. Then, before the Flash can get there and stop them, they use some kind of portal machine to vanish to places unknown.

While Caitlyn shrugs her shoulders, Cisco lights up.

“I had an idea, actually.” He wheels from one screen to another, where he already pulled up schematics for some kind of device. “You remember when you first started figuring out travel through portals and I cobbled together some things to help you with it?”

Barry nods. It had been a hectic time for all of them, and Barry honestly can’t quite remember what all Cisco came up with back then.

“So, I built this device that was supposed to tell me if and where someone opens a speed portal. Never got around to testing it, but I think I might be able to adapt it so not only speed portals show up, but other ones, as well.”

Barry beams back at his best friend. “That sounds awesome.”

“Right? I just have to re-calibrate it, set up the parameters, maybe change some of the wiring… But it should be good to go by the end of day, I think.”

It doesn’t yet give them a plan on how to defeat these people, but it’s something, at least. It gives them a way to more information and as scientists, all three of them appreciate the step in the right direction.



Barry is almost on time for his shift at the station and is promptly sent to the bank he’d been at a good hour before. There isn’t much new information to be found, and the day runs long with paperwork to handle and tests to run in the CCPD’s laboratory and stale coffee during his breaks.

He returns to Star Labs in the early hours of the evening, finds his two friends with three containers of Chinese take-out and happily takes the unclaimed box of curry. “Any updates?”

Cisco nods, waves his chopsticks towards his computer. “I got the thing set up. Should be good to cover anything in a 250 mile radius from here. I think. Didn’t test it, though.”

Portalling isn’t an easy feat for either of them, so Barry gets that Cisco has so far forgone running tests. He doesn’t fancy doing it himself right now, either.

They fall into easy conversation about Barry’s day at work, about a news article Caitlyn read, about some gossip Cisco heard when he went out to get food.

When the computer chimes, Cisco’s brow furrows and he wheels himself over to look at it. “Did Kara say anything about wanting to visit?” he asks Barry, tapping away at some keys.

Barry shakes his head. “No. Why?”

Cisco waves his hand around. “Because the alert I just got indicates a portal has been used. But the readings seem to align with the parameters I set for the initial use; portals created by excessive speed. As far as we know, the robbers’ portals are made by technology, not speed.”

Barry has already changed into his Flash suit. “Show me where, I’ll check it out.” Even if it has nothing to do with the string of robberies they’re trying to stop, he’s curious about who just entered this world.

The coordinates Cisco sends him to are a fair bit out of the city. The densely populated urban landscape changes to suburbs, then to lone farms. Barry rushes past, adjusts his steps to the changing ground, his speed to the free space ahead of him.

When he arrives at the place where Cisco’s software picked up the portal, there is little to see – except for a dust cloud starting from nowhere and leading west. It hadn’t been raining these past few days, and Barry knows all too well the dust a speedster can kick up in an environment like this.

He follows the trail, glaringly obvious as it is. It doesn’t take him long to spot its end, the cloud getting thinner before the wind manages to finally disperse it.

The woman he finds in the middle of a dusty field at the beginning of October isn’t Kara Zor’El.

Because there actually is a woman around his own age at the end of the trail. But where he’d expected blonde hair and a red cape, he finds something different entirely.

The woman in front of him is quite a bit smaller than himself – maybe of a height with Felicity, if she’d ever take those heels off. She’s got dark skin, even darker hair that curls out from underneath a riding helmet.

A riding helmet she apparently needs, seeing as she’s holding the reins of a caramel horse standing next to her.

Barry doesn’t know much about horses. Sometimes, for special cases, police units on horseback are called in – but even then, Barry doesn’t really interact with them. He can still tell that it’s tall, and well-kept. The caramel fur is shimmering, the black mane and tail tangled up from the wind.

While the horse throws its head at his approach, the woman doesn’t seem to notice him. She has her eyes closed, one hand stretched out towards the way her and Barry had come from, brow furrowed in concentration.

The horse stomps a foot and she lets go of the reins to absent-mindedly pat its neck. “It’s all good, I’ve almost got it.”

A second later, something whooshes past Barry far too close for comfort before landing in her hand. “See? Told you I’d-” she cuts herself off mid-sentence when she opens her eyes and finds the Flash standing in front of her.

Her eyes dart over to her horse before settling on Barry with a set determination. “Can I help you?”

“That’s usually my line,” Barry replies, because that’s not the reaction he usually gets. Not that he often finds women and their horses travelling through portals, but still.

He finally manages to get a proper look at the thing that almost chunked into his head. A curved piece of metal, slightly larger than a hand. It’s bronze in colour, but at a glance it’s hard to tell if it’s really bronze or just chromatized. “What is that?”

She looks at the piece of metal, then off-handedly gestures towards the horse with it. “A horseshoe,” she offers easily. “He lost it. It’s fine, though. I can still get him home and outfitted there.”

“How did you get it? It just flew into your hand.” Because yeah, even Barry who grew up in a city and has never been around horses knows what a horseshoe is.

Her brows furrow, and for a second, there is clear confusion in her face. “No, it didn’t,” she says, snapping her fingers. “I picked it up from the ground.”

No,” he replies, drawing out the word. “You held out your hand and it flew into it, almost hitting me in the head.”

She snaps her fingers again, and again, and again. With each snap, the groove on her forehead grows deeper, the confusion more apparent. It’s like watching someone struggle to get phone service far away from any civilization.

She finally abandons her snapping, turns her attention back to Barry. “Who are you supposed to be, anyway?”

Barry doesn’t think of himself as a conceited person. It’s simply a matter of fact that pretty much everyone knows him. But then again, if she’s from another universe…

“I’m the Flash.”

She tilts her head, considers his words. Slowly, like testing a theory, she lifts the horseshoe she’s still firmly grasping in her hand and pokes Barry with it.

Barry lets her.

Whatever experiment this was, whatever results she’d expected, Barry can’t tell anything out of the ordinary. Except for the fact that her confusion seems to grow as Barry allows himself to be pushed back a step.

Looking somewhat confused but more annoyed at it than put on edge, she slips the horseshoe into one of the saddlebags and holds her hand out to Barry to shake. “I’m Hazel, this is Arion.”

Barry shakes her hand. “Nice to meet you.”

“I don’t know where to put you,” she says, then crouches down to pick up some soil, only to let it flow through her fingers and back onto the field. “Hells, I don’t even know where to put myself right now. Where are we?”

So, Barry explains things to her. He explains that running fast enough might cause wormholes or people might use technology and even magic to jump universes. He talks about the multiverse, how it all connects to each other.

Hazel listens to it all, nods here and there. She doesn’t seem too convinced by his explanations, but not too surprised, either.

“Where are we, then?”, she asks. “Because you’re speaking English. By accent alone, I’d put you somewhere in the Midwest?”

Barry grins at her. “Yeah, exactly. We’re close to Central City.”

“Come again?”

“Central City?”

Hazel shrugs. “Never heard of it.”

And that’s… odd. There’d been a string of differences between the worlds he’s been to, sure, but the cities were mostly the same. “Where are you from, then?”

“San Francisco area. Was just heading back home from New York.”

“I’ve never heard of either of these places,” Barry tells her. “Are those big cities?”

Hazel actually laughs a bit at that. “Yeah, this definitely is a different world. Everyone has heard of New York where I’m from.”

There must be big deviations then, between his world and hers. Which brings Barry back to the question on how she got here in the first place. She’s too surprised by the whole ordeal to have done this before, to have gotten to his world on purpose.

Cisco already said that it’s probably a speed portal, but Barry wouldn’t know how to factor the horse into that equation. Maybe some different form of magic? Then again, she did just say she’d been travelling.

“So, are you a speedster or magic or something?”

“Well, I can usually do magic, but I can’t feel much of that power right now.” She pats her horse’s flank. “He’s the speedster.”

“Your horse?”

“Yeah. Fastest horse alive.”

Barry tries his best to take it in stride. Speedster horse. Sure. Whatever.

“So, if I want to get back home, I just have to hit terminal velocity again to pop back?”

Barry shakes his head. “Not that easy, I’m afraid. More likely than not, you’ll end up in yet another world. But don’t worry. We’ve got technology to help with that.”



The trip back to Central City takes longer than the trip out to the field, mostly due to the fact that Hazel doesn’t want to push her mount while he’s missing a horseshoe.

They’re still fast enough that keeping up a conversation is near impossible with the wind ripping each word out of their mouths and off into the fields. Instead, Barry updates Cisco and Caitlyn who answer him with a barrage of questions Barry hasn’t yet had time to ask.

Central City has been Barry’s home his whole life, but Hazel looks around with curiosity as they draw near.

It takes some coaxing to get Arion into the STAR Labs building. “I freed him from imprisonment,” Hazel tells Barry as she coaxes the horse through the hallways. “He doesn’t really like buildings.”

Finally, they get to the lab where Caitlyn and Cisco are waiting. Both scientists immediately get off their chairs and approach them, smiles on their faces, curiosity in their eyes.

“Hi, I’m Caitlyn. It’s nice to meet you.”

“This is so awesome. How did your horse become a speedster? I’d love to run some tests on him. Would it be cool if I drew some blood? I’m Cisco, by the way.”

Hazel looks between the two, then over at Barry, who just shrugs. “Nice to meet you, too,” Hazel tells Caitlyn. “I’m Hazel, this is Arion.” She turns to Cisco. “He was born this way, it’s genetic. No, you may not draw his blood.”

Cisco looks both crestfallen and all too ready to argue. “But imagine what we could learn from that!”

“I don’t care.”

“But…”

Caitlyn interrupts her friend, even though her own curiosity is still lingering in her eyes. “That’s entirely your choice,” she ensures Hazel. She eyes Arion sceptically, whose hooves are clacking ominously every time he raises a leg in restlessness and puts it down again. “Should he be in here?” The horse throws his head.

Hazel pats him.

Barry is somewhat impressed by the calm she exudes, the confidence with which she handles this animal that’s quite a bit taller and stronger than herself. There is no fear in her motions, no hint of even the possibility of harm coming at her that way.

“I’d love to take this outside, honestly. I don’t suppose your fancy lab comes with horse stables?”

The closest thing to horse stables they have are the cells on the lower floors, but Barry doesn’t think Hazel would appreciate the suggestion. Caitlyn has a better one, anyway.

“No. But we have bike sheds out towards the river that nobody ever uses.”

It’s not the best in regards to keeping things away from prying eyes, but they head out there, nonetheless. The bike sheds are tucked away underneath some trees, right next to the large parking lot few people ever use.

Barry dashes off to get some straw and before long, they’ve got a temporary shelter for the horse.

Hazel takes off his saddle, then his bridle. From the bags hanging from the saddle, she pulls a pair of brushes and begins brushing him down. “Tell me about your world,” she asks nobody in particular. “I want to know how different it is from my own.”

It’s easy to get talking.

They quickly notice that for all the differences that smacked them in the face at first glance, their worlds aren’t that different, after all.

The basic layup of their earths is the same, the continents, the countries. They go through a list of cities and they seem to be the same on the other continents, only differing on US-American soil.

Both sides clam up when it comes to superheroes, the magical, the supernatural, the otherworldly of their worlds. Careful, because neither side quite knows what to say, what to keep a secret.

“Vigilantes aren’t really a thing where I’m from,” Hazel says slowly. “Neither are Superheroes, the way you describe them.”

“But you did say you’ve got magic,” Barry remembers.

Hazel shrugs. “Yeah. Not too many people do, but still enough to form communities. We keep it more on the down-low, though.”

Communities. Barry has to smile as he thinks of Team Arrow over in Starling City and even Kara in her very own world.

“I don’t think there are too many people with magical powers, here. It’s mostly mutated enhanced physicalities or very advanced technology,” Caitlyn offers. “And sure, there’s a fair bit of community, but it’s mostly each hero having their own team to back them up and coordinating with other teams on bigger cases.”

“That sounds less like community and more like co-workers,” Hazel states plainly.

Cisco, who’s still a bit testy at his experiments being shot down, scowls at her. “So what? You do sing-alongs and game nights?”

Hazel meets his gaze, calm and unafraid, not raising to the bait for even a second. “That’s exactly what we do. We meet up at least once a semester to play capture the flag, to have a communal meal and to gather around a campfire to sing the night away. We wish each other happy birthday and say congratulations on the new job and complain about the new colleagues and send postcards and whatever else.”

Barry doesn’t know if she’s being sarcastic or not. He does know that he does none of those things with Oliver.

Dusk passes into night, and before long, tiredness slows their conversation and makes their movements sluggish.

When Barry offers Hazel his pull-out couch to sleep on, she shakes her head with a smile. “I’ll stay with him,” she says, pats Arion’s side. She fishes a blanket out of one of the saddle bags, and even a small pillow. “You don’t have to worry about us. We’ll be fine.”

They leave them there, then, the girl and her horse.

Barry, Cisco and Caitlyn slowly walk over to the parking lot.

“She’s a peculiar one, isn’t she?” Cisco says once they’re safely out of hearing range.

Barry snorts. “Lucky we’re all so normal.”

Caitlyn pats his arm. “Leave him be. Cisco’s just mad she won’t let him run his tests on her horse.” She gets into her car, drives off.

Cisco looks at Barry, affronted. “Like she isn’t curious about it, as well!”

Barry grins, watches his best friend get into his own car and drive away.

Yeah, they’re lucky they’re all so normal.

Notes:

Sooo....
Thoughts? Opinions?
This is completely written and mostly edited. I'm planning to do an update every 8 days (and am fairly positive that I'll be able to keep to the schedule.
Have a great day, stay safe.
💜💚🌻