LXP: While most of this crossover is based on the 1989 Disney film The Little Mermaid, I have also taken some elements and plot points from these other sources: the Disney Broadway musical, the 1975 Japanese anime film, and "Ariel's Secret" (children's book) by Melissa Lagonegro.

I do NOT own any of the mentioned above, or Miraculous: Tales of Ladybug and Cat Noir.

So, without further ado (drum roll)...

CHAPTER ONE:

LEGENDS OF THE SEA

Once upon a time, there were two races who lived in an uneasy existence with each other.

The humans, who walked on land and travelled on great wooden ships, were divided into separate kingdoms, each with their own rules, beliefs, and traditions. Humans were often believed to be reckless seekers of wealth, glory, and heroism. But there was also kindness, courage, selflessness, and compassion to be found in them.

The merfolk, with their long, fish-like tails and magical singing voices, lived in a single kingdom at the bottom of the sea – a glistening paradise called Atlantica. They were fearful of the world above the waves, and quite content to keep to themselves in their undersea hovels. Though the merpeople were not warriors, they did anything to ensure the protection and secrecy of their home.

A thousand years ago, the only thing the two worlds shared was an enchanted crystal known as the Miraculous. Granted unto both races by the sea god Poseidon, the Miraculous was the source of all magical power. It was capable of controlling the ocean currents, shifting the plates in the earth, and bending the winds to its will. Poseidon foretold that the Miraculous would unite the kingdoms of humans and merpeople into one realm, but warned them of the crystal's devastating powers should it fall into the wrong hands.

While this inspired some hope for the two races, there was still too much fear and mistrust between them. Then, one day, two kings came together to decide the fate of the Miraculous: Sotarius, the Human King of Agreste, and Triton, the son of Poseidon and the Sea King of Atlantica.

It was agreed between both rulers that the Miraculous be split into two pieces and safeguarded by the two kings and their descendants. The Ruby of Water went with Triton to Atlantica, and the Emerald of Earth stayed with Sotarius and the humans.

As the centuries passed, the legend of the crystal and Poseidon's prophecy faded from living memory. Humans were deemed as dangerous to the merpeople, and so they forbade all contact and interference with the surface world.

Likewise, mermaids were labelled as creatures of myth by the humans. Many a sailor had claimed to have seen or been saved by a mermaid at sea, but such tales were regarded as delusions of grandeur.

But all of that was about to change...

The Gabriel, the finest ship in Agreste's royal fleet, plowed through the water with the grace of a swan and the strength of a whale.

Prince Adrien sat atop of the ship's bowsprit, dangling his bare feet over the enormous expanse before him.

The sky was nothing but a shroud of bright-grey, turning the reflective sea into a rippling blanket of shady blue. The wind carried the scents of salt, fish, and soaked wood. White sea foam crashed against the hull and went flying into the air, leaving wet mist in its wake.

Adrien smiled and laughed as the sea spray tickled his feet, and he looked down at the mermaid figurehead at the front of the ship. Though she was made entirely of marble-like wood, she was fair and happy in every way. Adrien imagined that she found the cold water exciting as well.

He closed his eyes as the wind tugged at his tousled mop of golden hair, and just listened.

Behind him, the prince heard the vigorous stomps of several boots on the wooden deck. Amidst the stomping were the grunts and calls of sailors tending to the Gabriel's sails, or otherwise heaving the big net of fish up the starboard side.

As they worked, some members of the crew were joining their deep, choral voices together in a rhythmic shanty:

"I'll tell you a tale of the bottomless blue,

And it's hey! To the starboard! Heave-ho!

Look out lad, a mermaid be waiting for you

In mysterious fathoms below!

Heave-ho!"

Adrien hummed along to the song, swaying back and forth in tune with the ocean breeze.

"I'll sing you a song of the King of the Sea,

And it's hey! To the starboard! Heave-ho!

The ruler of all of the oceans is he,

In mysterious fathoms below!

Fathoms below-oh, below-oh!

From whence wayward westerlies blow,

Where Triton the king and his merpeople sing

In mysterious fathoms below!"

Suddenly, Adrien felt something squirming in the inside pocket of his white jacket.

Opening his emerald eyes, which appeared dull in the pale daylight, Adrien looked down and opened his jacket a smidge.

A tiny, black head with pointy ears poked out of the pocket and stared up at the prince with sharp green eyes resembling those of a cat.

But he wasn't a cat at all. He was a kwami, a rare type of species that came from the same kind of magic that created the gods. Or so the legends said. Adrien wasn't entirely sure if they were real or not, but Plagg – the black-cat kwami snuggling in his pocket – was real enough for the prince to guess that he had to have come from some kind of magic.

"Adrien, do we have to stay here and listen to all this racket?" Plagg whined in a scratchy voice. He flew out and stretched his paws and legs with a gloomy yawn. His tiny body was very disproportionate to his bulbous head. "Seriously! I can't even take a decent cat-nap in the middle of nowhere!"

Adrien smirked, knowing his little companion's penchant for being lazy. "Get real, Plagg," he said. "Why would you want to take a nap through all of this?" He gestured to the broad ocean before them. "The salty sea air, the wind blowing in your face, the endless horizon..." Adrien inhaled deeply and let out a relaxing sigh. "It's a perfect day to be at sea!"

Plagg glanced over the prince's shoulder, and a fanged grin grew on his face. "I'm not too sure your nanny would agree with you," he said, pointing out with his paw.

Adrien turned the moment he heard a terrible retching sound.

Sure enough, his royal advisor and family caretaker, Lady Nathalie, stood at the port-side railing, her heeled shoes almost inching off the deck as she bent over.

"Nat?" Adrien called. "Are you okay?"

The woman braced her hands on the railing and lifted herself back up. Her black hair, usually done up in a tight bun, had some loose strands blowing about in the breeze. Her sharp, crane-like face was a queer shade of green, and there were dark circles underneath her spectacles.

But Nathalie offered the prince a professional, expressionless stare and muttered, "Yes, Your Highness. Simply... delightful." Just then, her blue eyes shot wide open, and she heaved over the side once again.

Adrien cringed, suddenly feeling sorry for the woman, despite his earlier reluctance to bring her along in the first place.

Unlike everyone else on this ship, Nathalie wasn't accustomed to sailing. She, however, had been adamant in her decision to accompany the prince to the kingdom of Rossi. Adrien knew it was only because Nathalie wanted to pick out a suitable bride for him. Everything his advisor ever did was to ensure the stability of the kingdom of Agreste... and that included helping its future king settle down and start a family.

Adrien turned back to the horizon, trying to drown out those melancholy thoughts of marriage with the crew's upbeat singing and the soft thrush of the waves against the ship.

But it didn't work. Adrien kept thinking back to what his father, King Gabriel, had told him upon his deathbed:

Agreste needs a queen, Adrien, as much as it needs a king. You cannot rule a kingdom alone, so you must choose a princess worthy to rule at your side. Choose wisely, my son, and always remember your duty to your people.

Adrien sighed heavily. He was only seventeen, and his coronation wouldn't happen until he came of age at eighteen. That was only a few months away. That meant Adrien only had a few months to choose a bride... or he would have no choice but to let Nathalie choose one for him once he became king.

He hated the idea of potentially losing his freedom. If he had his own way, Adrien would never be king at all. He would forever stay on a ship, going on adventures across the sea. The only people he would rule over would be the brave men and woman onboard his vessel, who would address him as "captain" rather than "Your Royal Highness". That was the life Adrien wanted; the life he was born to live. The life of a sailor.

But his father, as strict as he had been with the rules, had been right about one thing: Agreste needed its rightful ruler to guide them through the coming years.

Adrien fingered the emerald ring on his right hand – the last thing he had left of his noble father. The band was made of black metal, and the large emerald gleamed brightly despite the lack of sunlight.

It was the ring of Sotarius, the first king of Agreste and Adrien's ancestor. The prince was the last of his line; the only heir to the throne. With both of his parents gone, Adrien had to uphold his "duty to his people" now. As much as it pained him, he knew it would be selfish and disrespectful of him to throw away everything his family worked for.

A great splash erupted beneath the prince's feet, soaking his rolled up trousers with cold water.

The shock sent Adrien into a fit of surprised laughter, but poor Plagg shrieked from the rain of mist.

"GAH! I have to get to someplace warm... and smelly!" The kwami zoomed away in a streak of black and vanished somewhere inside the ship.

Adrien rolled his eyes and used the rigging to pull himself up. Balancing carefully on the bowsprit, he made his way down and stepped back onto the main deck. Then he found his sailing boots and slid his dripping feet into them.

Time to come back to the real world, Adrien thought as he walked over to observe the crew.

Many saluted the prince before returning to their jobs. Most of the younger men were up in the two masts, ensuring that the sails weren't getting too loose in the wind. The older and more experienced sailors were busy unloading all of the fish they had caught into barrels, and rolling them carefully into the ship's hold belowdecks.

Suddenly, a sharp cry pierced the air.

Adrien looked to the starboard side to see a dark-skinned boy wearing a red bandana.

He was struggling to pull onto a rope that had untangled itself from the rigging. The rope was attached to the main sail, so the harder the wind blew, the more the sail billowed, taking the rope and its holder with it. The boy let out a startled yelp as he went sliding and skipping along the deck.

Adrien immediately sprang into action, rushing to the boy's side and grabbing the rope with both hands. "I gotcha!" the prince called. Then he shouted for a couple more crewmates to lend a hand.

Together, they brought the rope back and secured it around one of the wooden anchors along the railing. Once that was done, the boy with the bandana patted Adrien on the back with relief.

"Thanks, dude," Nino sighed. "I thought that sail was going to snap off and carry me away."

Adrien chuckled at his best friend and first mate. "No problem," he said before turning to his lingering sailors. "Let's get all the sails properly secured! The wind's picking up again!"

"Aye-aye, Cap'n!" some of the men shouted in unison before scampering up the shrouds.

Nino pulled off his glasses and wiped his forehead. His golden-brown eyes bore a twinge of sheepish guilt. "Some first mate I'm turning out to be," he grumbled. "I'm barely more than a decent sailor compared to the rest of these guys."

Adrien gave him a brotherly side-hug. "Don't be silly, Nino. You know I can always count on you. And you are a good sailor. That wind was just a nasty breeze, that's all."

Nino pushed his glasses back onto his nose with a smile. "Yeah, well... no breeze can get the best of me, that's for sure." He planted his fists on his hips and puffed out his chest proudly.

Adrien grinned.

A bearded sailor beside them nodded. "Aye, we've got a fine, strong wind an' a followin' sea today," he commented. "The Sea King must be in a friendly mood."

The prince's eyes brightened. "The Sea King?" he asked, recalling the crew's shanty. "As in... King Triton?"

"Triton? Bah!" croaked a red-headed man who was pulling fish out of the big net. "He was ancient times, boy! Lived nigh a thousand years ago! But every good sailor knows there's always a Sea King rulin' the merpeople."

Adrien's attention piqued. "Merpeople..." he murmured.

He had grown up listening to his mother's stories about mermaids and merman in their underwater kingdom. Adrien thought back to the ship's figurehead, picturing it coming to life and singing with the voice of a thousand angels.

And then, there was that day on the beach ten years ago, when...

The prince's imagination was broken by an all-too familiar tone of indifference.

"Merpeople?" Nathalie scoffed, smoothing out her hair as she stepped hazily towards Adrien and Nino. "Oh, please, Your Highness... Don't pay any attention to such nautical nonsense."

Adrien frowned with a huff.

Another one of Nathalie's annoying alliterations to add to the list: nautical nonsense, a sailor's superstition, a marine myth...

"It ain't nonsense – it's the truth!" the redhead snapped. He stood up and walked over to the group, wriggling a fish in his hand. "I'm tellin' ya. Down in the depths of the ocean, they wait for human ships to pass over 'em. Then, they sing their enchanted songs to lure sailors to their doom!"

Adrien blinked. Nino gulped. Nathalie snorted.

"Just think," the sailor continued, his tone becoming menacingly low, "the last thing ya hear on this earth is the sweet melody that fills yer heart with love and devotion. Then, before ya know it, yer ship crashes into the rocks, and ya feel the water crushin' in on ya as a pair of soft, cold hands drags ya down to the darkness." The sailor grinned a toothless grin. "But don't worry – they don't get all of ya. They leave some of ya behind for the sharks they keep on leashes."

Nino suddenly grew a shade paler.

Adrien blew out a raspberry. "That's ridiculous!" he stated.

"Precisely," Nathalie noted smugly.

"Everyone knows that sirens lure sailors to their doom, not mermaids," Adrien explained.

Nathalie gaped at him. "Your Highness..."

"Cap'n's got a point," said a nearby young man.

"Yeah, mermaids don't want nothin' to do with the likes of us anymore," said another, pointing downward. "That's why they stay down there – on the sea bottom."

Nino seemed to ease up a little. "So... no pet sharks?" he asked.

Adrien chuckled. "None whatsoever, my friend," he said. "Trust me."

Nathalie let out a moan... and then ran straight for the railing with her hand over her mouth.

The prince and the others turned away with sickened expressions.

Then, Adrien clapped his hands. "All right, gentleman, back to work!"

The crew marched away, and Nino tipped his bandana to Adrien before zipping up the stairs to talk to the helmsman at the wheel.

The prince took a spot at the railing, gazing once more at that beautiful horizon in the distance. Endless, landless, and free.

And full of possibilities.

Adrien felt something land gently on his shoulder, and he caught a whiff of something foul. He glanced down to see Plagg nibbling on a chunk of camembert – the kwami's favourite food, and the nastiest-smelling cheese in the world.

"So..." Plagg said between bites, "what'd I miss?"

Adrien turned his head to face the wind so he wouldn't have to smell that stinky cheese. "Oh, nothing much," he replied. "Just talking about mermaids."

"Mermaids? Hmm..." Plagg took another big mouthful of camembert. "You thinking what I'm thinking?"

A memory came back to Adrien: a warm beach, a seven-year-old boy, and a large, fish-like tail disappearing into the water.

"Yeah," Adrien said.

"Some cold caviar would be really good right about now," Plagg said.

Adrien snorted. Typical.

He stared down at the flapping waves below him, and he smiled. If only he knew...

LXP: If you guys are wondering what Adrien means by that, I'm afraid you'll have to wait until Chapter 3 to get answers.

Sorry that this chapter was a bit of an info-dump, and the next one will be too. But I promise I'll keep it all as interesting and significant as possible.

I don't own "Fathoms Below" (both the film version or the Broadway version)

Stay tuned!