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Published:
2025-05-02
Updated:
2026-02-13
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121,794
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41/51
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The Glowing Tide

Summary:

There are many things to be cautious of in their watery world, from the merran to the Ryuu, but none so terrifying as the glowing tide—just one splash and that’s all she wrote, you’re no longer human but another monster to menace those trying to survive on the waves.

Hiro, unfortunately, has fallen victim to the glowing tide—and his only hope of survival is a deep-sea merran that goes by the moniker of Ghost.

Notes:

Ladies and gentlemen, assorted fish, time for another one of these funky BH6 AUs!  If you’ve been following me elsewhere you’ve seen me mention this fic and do art for it before, and since last night I finished the climax chapter and there’s nothing left but the denouement, it’s time to start posting. \.o./

So this is more accurately called a mer AU over a mermaid AU since we’re going to be following some boys around—merran are my own take on the whole mermaid idea and there’s going to be some specific differences and speculative biology and such and that makes me happy.  As for the setting, if you’re familiar with the game Sunkenland or the movie Waterworld then you’ve already got the idea.

Updates will be every Friday, and while I was torn on doing music titles for chapter titles, I think I’ll leave that for special occasions (definitely want to have “Beyond the Sea” as a chapter title) and focus on the idea I had a while back of using nautical terms—have some websites bookmarked for that so that works, time to get fishy. :D

Big Hero 6 © 2014 Disney

Chapter 1: Inundation

Summary:

Inundation - to overwhelm or flood.

Notes:

(See the end of the chapter for notes.)

Chapter Text

 

Part 1: Acclimating


“Come on, Hiro!”

“No, thank you,” Hiro Hamada said, watching his brother Tadashi splash around.  “Dry land for me, thanks.”

“You mean the boat—dry land’s at a premium.”

“I’m just saying the water looks questionable,” Hiro insisted as Tadashi swam back over to their little skiff—it had taken some convincing to get it and a lot of elbow grease to patch it back up and get it running, but it was great for short scavenging trips.

“It’s not glowing, that’s my bare minimum,” Tadashi said, hauling himself back in.  “And look—me and Fred scouted this place a couple days ago, it’s perfectly safe, and it’s shallow enough for us to practice your swimming.”

“I could have done this back on the flotilla, Tadashi.”

“Yeah, but you didn’t—now it’s time for drastic measures.”

“Nope,” Hiro said.  “I’m perfectly fine with not getting wet, when we get to the Rockies that won’t be a problem, thanks.”

“The flotilla won’t circle back to the Rockies for years, Hiro—you need to get better at swimming.”  Jump back in, making the skiff rock—pop back up and grin at him.  “Come on, you can’t tell me you’re not a little tempted.”

Hiro bit his lip, considering—okay yes there was a lot of goodies underwater—ever since the rains and the floods and the massive tsunamis had rendered most non-mountainous land seafloor it had left a lot of unclaimed stuff abandoned down there.

It was just there was a lot of water, and it was more than a little intimidating.

“Come on, I’ll be right here,” Tadashi assured him.  “Just slide in, we’ll practice your floating first.”

Grimace, deep breath—gingerly slip in, clinging tight to the side of the boat and hissing when he got wet.

“Yeesh, are you part cat?” Tadashi teased, looping an arm around Hiro’s chest.  “Okay, ready?  Let go.”

“What if I don’t want to?  What if this was enough?  This feels like enough.”

“Are you really going to make me go diving by myself?”

“Hey no wait no one said anything about diving!”

Tadashi sighed.  “Okay, climb back in, hand me my goggles.”

Hiro was more than happy to oblige, scrambling back into the skiff and all but throwing the goggles at Tadashi’s head.

“Oof, trying to kill your own brother!” Tadashi dramatized, tugging the goggles on—took several quick breaths before one big one, dove down.  Hiro eased over, watch as his brother swam low over the bottom—wow he was right, it was relatively shallow here.

Not that that made it any better—shiver a little in the light breeze, look around at the featureless flat ocean—good thing Tadashi had a compass, because Hiro was totally lost.

Start at the splash, look over to see Tadashi levering a few items up into the skiff.  “You missed your calling as a merran, I hope you know that.”

“Not saying I wouldn’t rock it, but then who’d keep after you?” Tadashi asked, heaving himself up.  “You’re a magnet for disaster, I need you to know this.”

“Not on purpose—it just sort of happens.”

Tadashi laughed at that, squinted at the distance.  “Okay, one more dive and then we’re going back—I don’t like how those clouds look.”

Hiro looked in the direction Tadashi indicated, didn’t really see the problem—those clouds were miles away, they’d be long-gone before they drifted over.

“You know, bro, sometimes you worry about the weirdest things,” Hiro told Tadashi when he climbed back in the boat.  “Terrified of clouds but perfectly fine with dragging your brother into a bottomless ocean.”

“Trust me Hiro, there’s a bottom to that ocean,” Tadashi told him.  “It’s just too far to see.”  Get the engine running, start motoring away.  “Miles beneath the surface, nothing but crushing blackness powerful enough to crush the flotilla into a softball.”

“Gee, thanks, Tadashi, this information makes it so much better.”

“Glad you agree,” Tadashi said, looking back at the clouds as a breeze picked up.  “Now let’s get out of here.”

 

Tadashi’s worry was right on the money: the storm caught up with them well before they got back to the flotilla.

Thanks, Tadashi, I really wanted to get wetter,” Hiro groused, soaked to the skin.

“See?  If you had gone diving with me this wouldn’t have been nearly as wet,” Tadashi teased, trying desperately not to panic—this was bad, this was very very bad, he needed to get them back post haste.

This was not to be, unfortunately—couldn’t navigate via the sun, and the compass he had super-glued to the engine was slick with rain to the point it was unreadable.  They were lost, plain and simple.

The storm intensified, Hiro hanging on for dear life as Tadashi tried steering the skiff into the growing waves—finding the flotilla again was a pipe dream right now, right now the main focus was on not dying—

“Hang on, okay?” Tadashi called.  “Just hang on, we’ll get through this!”

Hiro looked back, grimacing—shifted to horror as he focused on something behind him.  “Tadashi!”

Tadashi looked, expecting to see some giant shark fin or other nasty—

Oh no.  No.  This was worse.

It started with little spangling lights where the rain struck, was almost beautiful as it intensified, all but illuminating the underside of the clouds and competing with the lightning.

The glowing tide.

“No no,” Tadashi breathed, focusing back ahead.  “Don’t worry about it!  We’re gonna make it!”

The boat bottomed out when they crested the next wave, both of them nearly flying out of the little skiff—gun it up the next wave, had to keep them from capsizing, had to keep them out of that glow—if they hit that water it was all over, that was it, they’d never be seen again.

Second wave jostled the engine, making it cough—hit it desperately, coax it back to life, gun up the next one—

Next one was too much, too tall, had already started curving when they hit the top—Hiro was too light compared to Tadashi and the engine, and the loot he had dove for—a lifetime ago, it felt like—had long since bounced out.

As such, the back end of the boat hit perpendicular to the surface, Hiro screaming as he was flipped away—

Tadashi lost a moment, hit his head on impact, tried to swim up to hit his head again on the boat—surfaced, gasping, clawing his way onto the capsized skiff, bracing himself as another wave hit—

Freezing in terror as the glow neared, intensifying—

Suddenly faded, leaving the belly of the storm black as the waters beneath.

“Hhh—Hiro,” he gasped, looking around frantically.  “Hiro!”

But there was no response.

Notes:

As for this first chapter...Hiro’s quoting Tantor from the disney Tarzan movie.  Also storms can blow in quickly on the water so Tadashi’s right to be concerned.