Fluttershy was diving underwater with a black wetsuit and a diving mask. She was the only one of the Rainbooms to have one of these masks, as the others weren't that interested in diving, although Sci-Twi did express interest in exploring underwater.
Today Fluttershy was swimming with the small, colorful fish (and eels), which she always enjoyed doing. But today would be different, with an unexpected twist.
"Fluttershy..." a female voice rang out. Fluttershy thought the voice sounded familiar, but maybe it was just her.
"Who's there?" Fluttershy was a little nervous.
"I am the Spirit of the Lake," the voice said. "I sense you are worthy of finding the legendary treasure of the Pirate Trio."
"The what?"
"You are the first person to swim in this lake who is worthy of possessing the treasure. I sense you have six friends who are just as worthy. Here." Seven keychains resembling seashells floated over to Fluttershy. "Attach these keychains to yourself in some way and you will be able to breathe underwater. You won't even need that mask anymore. Now, find your friends and claim the treasure!"
Fluttershy finished telling Sunset Shimmer, Sci-Twi, Rainbow Dash, Applejack, Pinkie Pie, and Rarity what had happened.
"Ooh, the legendary treasure of the Pirate Trio?" said Sci-Twi. "I've read about them. Three pirates who sailed that lake 667 years ago. They attacked boats that sailed there, until the Royal Navy sunk their ship and they drowned."
"Legendary treasure?" said Rarity. "There must be all kinds of beautiful jewels in there! And of course I'll split it with you 50/50!"
"I don't know..." said Sunset. "What if it's guarded by pirate ghosts?"
"G-g-ghosts?" said Fluttershy.
"That doesn't sound fun," said Pinkie Pie, looking equally frightened at the idea.
"If it was guarded by ghosts, would the spirit of the lake tell us to go find it?" said Rainbow Dash. "Even if it was the ghosts saying it, why would they tell us to go after it? Wouldn't they try to keep it hidden first, and defend it from anyone who found it on their own?"
"She's got a point," said Applejack.
"Who wants to test if these keychains will really make us breathe underwater?" said Sunset.
"What if they don't work and we drown?" said Sci-Twi.
"I'll do it!" said Rainbow Dash, naturally the most daring one. She attached the keychain to the necklace containing her geode, and stuck her head in a nearby fountain. She opened her mouth to breathe in...
"Well?" said Sci-Twi as Rainbow Dash pulled her head out.
"These totally work!" said Rainbow. "This is awesome!"
"Can we go looking for the treasure now?" said Rarity.
Sunset, Sci-Twi, and the Rainbooms met up at the beach of the lake, wearing their swimsuits, their geodes, and their keychains attached to them.
"Let's do this," said Sunset.
They walked into the water. Well, Rainbow and Pinkie ran. Once they were deep enough, they dove underwater. Fluttershy was a little nervous, but she took a breath and relaxed knowing the keychains worked.
They swam deep into the lake.
"Oh my gosh, this is so amazing!" said Sci-Twi. "I've never had the chance to see all this scenery in person before! Of course I've read lots of books about it!"
"This is simply divine," said Rarity.
"Yay," said Fluttershy.
"Hey Applejack, race you to that reef!" said Rainbow Dash.
"It's not a reef, it's the kraken!" said Pinkie Pie in a menacing sort of voice.
"There's krakens in here?" said Fluttershy.
"I'm just kidding, Fluttershy!"
Rainbow Dash swam to the reef and back with her super speed. "I win!"
"No fair!" said Applejack. "I demand a rematch, but without your super speed!"
"We're here to look for the treasure," said Sunset. "You two can race each other all you want once we've got it."
"Oh all right," said Rainbow Dash.
"Wait, listen!" said Sci-Twi. They could hear a voice in the distance.
"Rainbooms... Rainbooms... Come... Follow my voice... the treasure is this way..."
"That's the Spirit of the Lake," said Fluttershy. "She's the one who gave us these keychains."
"Well, we'd better follow her," said Rainbow Dash.
"Since when did anyone call us 'Rainbooms' when we're not onstage?" wondered Sunset.
They swam in the direction of the voice, and soon they came across a sunken ship.
"This must be the ship of the Pirate Trio!" said Sci-Twi. "I can't believe it! This is such a HUGE discovery! This ship is legendary, and was sunk hundreds of years ago!"
"Never mind the ship," said Rarity. "Let's find the treasure!"
They swam around the ship in search of a treasure chest.
"I found it!" said Pinkie Pie, who picked up a balloon and a bag of marshmallows.
"I'm pretty sure that's not it," said Rainbow Dash.
"Aha!" said Rarity. "I found it!" She opened the chest. It was full of gold coins and jewels. "Applejack, can you be a dear and haul this up with your super strength?"
"Right away, Rarity!" Applejack held the chest in one hand while swimming with the other.
As they swam out of the ship, the voice spoke again.
"We have been waiting for you, Rainbooms."
Three figures swam in front of them, and Fluttershy instantly realized why the voice had sounded familiar.
"You!" said Sunset.
"Yes, we're still alive," said Adagio Dazzle.
"No thanks to you," said Aria Blaze. "Those pendants you destroyed contained our siren powers, and kept us alive as humans for over a thousand years since that accursed unicorn banished us."
"Hey, that's my bag of marshmallows!" said Sonata Dusk, pointing at the marshmallow bag in Pinkie's hand.
"Finders keepers, siren!" said Pinkie aggressively.
"Anyway," said Aria, "before I was so rudely interrupted, a few minutes after our pendants were destroyed and we ran off the stage coz the crowd was throwing food at us..."
"Why do they always bring eggs and tomatoes to a concert?" said Sonata.
"Can you just shut up and let me speak?" Aria glared at Sonata. "A few minutes after, we started to age rapidly. To the age we would have been without the pendants."
"We barely made it here," said Adagio. "For when we sailed this lake 667 years ago, we put any sailors we came across under our spell and fed off their hate. Soon we gathered enough power to cast a spell on this lake to preserve our powers, in case we lost our pendants. Because our spell enabled us to breathe under the water of this lake, we hid here for a few years after our ship was sunk so they'd think we drowned."
"Wait... YOU'RE the Pirate Trio?" said Sci-Twi, who had heard of the sirens from her friends but never actually met them before.
"Damn straight," said Aria.
"So, when we got to this lake, our youth was restored," said Adagio.
"Just like that evil queen in that anime who imprisoned herself in a mirror just to regain her eternal youth!" said Sonata.
"Queen Nehelenia in Sailor Moon?" said Pinkie Pie. "I remember that! Funny she's the only villain in that show to neither die nor reform. I wonder if that'll end differently in Crystal?"
"...so was our ability to sing," said Adagio, as though Sonata hadn't interrupted again. "And we were able to enchant these seashells with the ability to breathe underwater."
"But if we leave this lake, we lose our power again, and age into dust," said Aria.
"I miss tacos," said Sonata. "They don't have any underwater! It's been a year since I last had any! Fortunately I stashed some marshmallows here just in case! They're so much better than seaweed or raw goldfish!"
"Goldfish?" said Fluttershy, who would never feed that adorable kind of fish to ferrets.
"So, we lured you here with our precious treasure to steal your magic so we could return to land, put everypony under our spell, and return to power!" said Adagio.
"We'll never let that happen!" said Rainbow Dash.
"It was a trap all along!" said Sunset.
"The treasure is real," said Rarity. "We'll defeat you ruffians again and leave with our prize!"
"I think not!" said Adagio. "We're not giving up our precious treasure even if we were going to let you leave here alive!"
"You heard her," said Aria. "Welcome to your watery grave!" She licked her lips as Sombra had when he was about to impale Spike.
The three sirens started singing. "Welcome to the show, we're here to let you know..."
Rainbow Dash swam around them in circles as fast as she could, creating a whirlpool that trapped them. The sirens used sound waves to disperse the whirlpool and blast Rainbow backward a bit.
Applejack grabbed Aria, still holding the treasure chest, and threw her into Sonata. Adagio blasted her with sound waves.
Fluttershy called a swarm of eels to wrap around Adagio. Aria and Sonata blasted the eels with sound waves, causing them to swim away. Then Aria swam at Rarity and tried to punch her in the face, but Rarity activated her barrier, repelling Aria.
"I see you've picked up some new tricks since we last met," said Adagio, and the three sirens tried to blast the Rainbooms with more sound waves just as Pinkie raised her hands. The sound waves exploded, knocking the sirens backwards a bit. Sci-Twi froze them with her telekinesis and threw them backwards, and they tried to swim away.
Aria was the faster swimmer. She grabbed Sunset's foot and pulled her back. Sunset felt pure malice and hatred from her, the likes of which she had only known when she had been transformed into a demon.
"Sunset Shimmer," said Adagio as she and Sonata swam over to her. Adagio grabbed Sunset's head with both hands. "How fitting. You were the reason the other Rainbooms defeated us. I guess you'll be the first." She opened her mouth to use her sound waves.
"Sunset!" The other girls swam toward her. Applejack dropped the treasure chest and aimed a punch at Adagio.
Adagio released Sunset and swam out of the way. Applejack's fist made contact with the bottom of the lake, and it split open into a crevice.
The treasure chest fell down the crevice.
"Oh no," said Pinkie, "this is gonna be one of those cheesy 'don't get the treasure we were searching for the whole story' kind of things, isn't it?"
"The treasure!" The sirens dove down the crevice after the chest and straight into the molten magma.
"Wow," said Rainbow Dash. "I can't believe they did that!"
"Wait!" said Sci-Twi. "How can there be lava underwater? It's not scientifically possible! The water should just harden the lava into igneous rock!"
"She's right," said Pinkie. "My sister Maud knows all about igneous rock."
"The lake is magic," said Rainbow Dash. "We'll just chalk it up to that."
The lava suddenly hardened.
"There you go," said Rainbow Dash. "The sirens are gone, so their spell broke."
"I wonder why the keychains didn't lose their power," said Applejack. "The sirens enchanted them too, and we can still breathe."
"Maybe our magic keeps this magic alive," said Sunset. "We DID connect it to the magic we picked up at Camp Everfree."
"Like some sort of battery charger," said Sci-Twi.
"I am thankful we made it out of that alive," said Rarity, "but... that treasure was so magnificent... and now it's gone... melted in the lava and now a mass of igneous rock... We came all the way down here and almost got smashed to pieces by the sirens for nothing!"
"Um... Rarity?" said Fluttershy. "I think I saw another treasure chest at the sirens' ship."
Author's Note
No, I don't have a headcanon for this. My headcanon goes the sirens aged into dust after their pendants were destroyed. This is just a sort of alternate ending fanfic.
Also, they do use "smashed to pieces" as a euphemism for "killed" in the show (Wonderbolts Academy). Ironically, the Storm King's death was literally him being smashed to pieces! Lol
And the sirens' defeat is a parody of an Archie's Weird Mystery episode with the pirate ghouls.
