This is a major world building chapter, so there's a lot of information to take in. Sorry for the info dump. Any questions you have will likely be answered in the next few chapters since they are also dedicated to shaping this world and introducing OCs. In any chapter where a new OC is introduced, I will include a character bio in the notes at the end of the chapter.

Wednesday, July 31, 1996

10:00 a.m.

"Why do I have to wear this blasted contraption?"

"It's what the Muggle people Above wear! You can suck it up for two weeks, Marius," Iulia snapped. "So help me, I will break every bone in your body if you get us caught because you don't like pants."

Marius scowled at her and continued fiddling with the trousers he'd found in his pile of clothes. He'd only been Above twice before, once for the traditional trip and once for a scouting mission three weeks ago.

"You should be grateful Alder got these for us at all," Iulia said, pulling on her own pants.

Marius snorted. "He's been pining after your dad for years, I don't think there's very much Alder wouldn't do for him."

"True," Iulia said thoughtfully.

She slipped on the shoes Alder had picked out for her and put the bag she'd found her clothes in inside her pocket. Gazing out at the rippling waves of the ocean, she thought of her parents and the siblings she'd left behind. Seventeen years ago, her family had been destroyed by the loss of her baby brother, and now she was here to get him back. "I won't fail you," she murmured.

"I'm ready, Princess," Marius said cheerfully.

"Don't call me that," Iulia sighed. "Do you have the Portkey from Alder?"

Marius held up a silver scale the size of his palm.

"Oh, Marius," Iulia whispered, "You used your own scale?"

"It'll get us as close to Privet Drive as we can go without tripping any wards or alarms," he said quietly. "We can't afford to screw up now, not when we're so close."

Iulia drew in a shuddering breath. "You're right, of course. Do you have everything? Your focus?"

Marius patted his back pocket, nodding silently. "I've got my weapons as well, I'm as ready as I'll ever be. Let's go get your brother back."

Iulia gave him a small smile and reached out to touch the proffered scale.

"Hadrian."

The strange pair disappeared from the beach without a sound, leaving behind no sign that they had ever been there.

1:15 p.m.

Harry Potter was not having a great sixteenth birthday. According to Aunt Petunia, he'd been about to burn the eggs when cooking breakfast, so she threw him out of the kitchen and made breakfast herself. He'd been allowed one scoop of eggs and a burnt piece of toast. He'd barely finished his milk when Aunt Petunia had whisked the plates away and sent Harry back upstairs. Having nothing else to do, he retreated to his room without a fuss.

Harry had been reading his Herbology textbook for the last few hours when Aunt Petunia opened his bedroom door.

"Yes?" he asked.

"The garden is in horrible shape. Go weed and water it," she demanded.

Harry sighed and put his textbook aside. Truth be told, it would be nice to go outside. He didn't mind taking care of the garden, weeding was a calming task for him.

"Yes, Aunt Petunia," he said.

She went to close his door and leave, but hesitated for a moment.

Harry raised an eyebrow. "What?"

"Happy birthday," she said shortly, yanking the door shut.

Harry stared at the closed door in shock. It was very unlike Aunt Petunia to acknowledge his birthday, she much preferred to pretend that he didn't exist at all.

Shoving the weird interaction out of his mind, Harry grabbed his trainers and descended the stairs, shoving the shoes onto his feet before exiting the kitchen. He shut the back door before retrieving gardening tools from the shed, enjoying the gentle breeze that greeted him.

Harry kneeled before the agapanthus section and began pruning the flowers and battling the weeds that sprouted there. Every so often, curls of hair would fall into his line of vision and Harry just frowned and tucked them behind his ears.

Something strange was going on with his hair and eyes recently. Ever since he'd returned to Privet Drive after the battle at the Ministry, his hair had been gradually lightening in shade until it was a light brown. His eyes, usually a deep forest green, had brightened until they became light green. Harry also thought his skin was a few shades paler, something he hadn't thought was possible. Since his hair was the most noticeable of the lot, Harry had told Aunt Petunia that he'd dyed it so she wouldn't ask questions.

Harry quietly hummed to himself as he worked. It was an unusually cool day, something Harry was grateful for as the minutes ticked by.

After a while, the sounds of an argument gradually increased in volume until Harry couldn't ignore it anymore. He stood up and brushed off his pants as best he could before investigating.

As Harry rounded the side of the house and approached the street, he saw two people standing on the sidewalk in front of number two. A girl holding a map was talking to a boy who looked quite frustrated with her.

"It's number four, right? Are you sure?" the girl was saying.

The boy exhaled sharply and said, "If you don't trust me, trust Alder, he's the one who told us where to go," he tapped the map in the girl's hand for emphasis.

"I know, I know, it's just that we've got to be sure. We can't have it getting out that we're looking for him!" the girl responded.

At this point, Harry was fairly sure that they were talking about him, which confused him to no end. He doubted they were Death Eaters, Death Eaters wouldn't have sent two teenagers to get him. They were also being fairly obvious, so Harry doubted that they meant him any harm. Nevertheless, he made sure that his wand was still securely in his front pocket before moving closer.

"Can I help you?" he asked.

They both started and turned to face him, the boy's hand making an aborted motion toward his back pocket.

"I — oh!" the girl gasped, her hand flying up to cover her mouth. The boy looked equally shocked, like he couldn't believe Harry was standing there.

"Can I help you?" Harry repeated, moving closer. He had no clue who these people were, but they weren't setting off any alarm bells in his head.

"Are you Hadrian — Harry Potter?" the boy blurted, getting an elbow to his ribs for his efforts.

"Yes," Harry said slowly.

"In that case, can we talk? It, well, it's kind of important," the boy asked. The girl still looked like she'd been hit by a Bludger.

Harry glanced back to number four, knowing that Aunt Petunia was the only one home, and made a split-second decision.

"I guess, do you want to come around the back?"

Both strangers nodded, so Harry led them to the garden and pulled out three folding chairs from the shed, giving one to each of them. They both carefully watched Harry set his own chair up and sit down before following suit.

"Listen, I have no clue who you are and what you want with me, but I'll hear you out," Harry told them.

Harry didn't know why all of his self-preservation instincts — the precious few he had — had flown out of the window, but something in him was reaching out to the strangers and he wanted to know why. He examined the pair in front of him as they glanced at each other, clearly wondering how to begin.

The boy was wearing a plain t-shirt and jeans, paired with trainers that looked brand-new. His long brown hair was tied back and he wore a necklace with a single tooth hanging from it. The girl was dressed similarly and she wore a locket clasped around her throat. Her black hair was also tied back and hung down to the small of her back.

"I'm Marius Mercator," the newly-named Marius began, looking at the girl.

"And I'm Iulia Aurelius," she said, looking closely at Harry's face. It seemed like she was waiting for a reaction from Harry, but Harry did not recognize either name and her face fell when that became clear.

"I don't really know where to start," Iulia said, one hand reaching for her locket. "I think we'd given up hope of ever finding you."

"Why were you looking for me?" Harry cautiously asked. One hand was on his wand just in case things went south, but he couldn't deny that his curiosity was piqued.

"This is going to sound crazy, but please hear us out," Marius said.

"I'm your sister, Harry," Iulia admitted.

Harry's mouth nearly dropped open. A well of forgotten and repressed feelings came rushing back like a tidal wave. For years, he'd dreamed of some unknown relation taking him away from the Dursleys, but when he'd gotten his Hogwarts letter and learned of his parents' true fates, he'd given up on that hope. He was the last Potter and nothing was ever going to change that.

"But — how — why — are you sure?" he finished weakly.

Iulia smiled tremulously at Harry. "You look just like our Mum, you know, there's no mistaking those eyes. She'll be sad to know that she cursed you with her uncontrollable hair, too," she said.

Harry tugged on a lock of hair self-consciously. Iulia didn't know what he'd looked like before the changes started happening. Did that mean he'd been under a glamour for sixteen years?

Iulia took a deep breath and closed her eyes, a few tears trickling down her cheeks. Harry uncomfortably shifted in his seat, crying girls always made him nervous.

"You were stolen," Marius said, taking over the narrative. "Your parents took you to London as part of the traditional trip all parents take their kids on. They were staying at a hotel when they were ambushed. When they woke up, the room was destroyed and you were gone."

"We looked for you everywhere. Dad was furious and Mum couldn't stop crying. The Guard had members stationed Above for months, hoping they could discover who had taken you and where you'd gone," Iulia told him. "Marcus took it especially hard, he was the one you favored, even over Mum. The Guard stayed here for two years, but Dad called them back home when it became too painful to keep looking."

There were a million questions swirling in his brain, Harry didn't have the slightest clue where to start. He had a family, apparently. A family he'd been taken from, a family who'd looked for him. A family he could've spent his childhood with. A pit of rage began simmering in his stomach, he was absolutely furious at whoever had torn his family apart.

Harry started with the simplest question he could think of, "Where's home?"

Iulia bit her lip and glanced at Marius. Marius sat up straight, gesturing to Iulia that he'd answer.

"This is where it might get to be a little too much for you to swallow," Marius said apologetically.

Harry snorted. He'd taken the news that he was a wizard rather well, and that had been life-altering.

"We call our home Lyonesse, but you might know it better as Atlantis," Marius revealed.

This time Harry's mouth did drop open. "You mean to tell me that you live in a city that's underwater?" he sputtered. "How do you breathe?"

"Lyonesse is fully underwater, yes, but it wasn't swallowed by the ocean like the Atlantean myths would have you believe. Our ancestors built the city for us when it became clear that living Above was too dangerous," said Marius.

"As for how we breathe," Iulia interjected, "We survive underwater because we're not completely human. We have human forms, but we rarely use them. Our Mer forms are what we spend our day-to-day lives in."

"Like the merpeople in the Black Lake?" Harry wrinkled his nose.

"No!" Marius exclaimed, making Harry startle. "Sorry," he apologized, "The Mers that live in the Black Lake and in other places around the world are distant ancestors of ours, but they've corrupted themselves with Black magic. The Mer form we have look just like our human forms, but with a tail instead of legs."

"They look like dolphin tails, but with scales," Iulia explained.

Harry lowered his head into his hands, rubbing his temples. This was a lot to take in at once. Part of him wanted to write them both off as crazy, but a warm feeling had started growing in his chest once they had started talking about Lyonesse and Mers. That, more than anything, convinced him that they were telling the truth.

Harry decided to leave the whole 'I'm secretly a Merman' thing alone for now. He wanted to know why they hadn't come for him before now.

He took a steadying breath. "If the Guard — whatever that is — stopped looking for me after two years, why are you here now?"

Iulia immediately groaned, "Don't get him started on the Guard, I beg you."

"Shut up," Marius glowered at her. "The Guard is Lyonesse's army, for lack of a better word. We guard the city, make weapons, fend off predators, and hunt for food. Usually sharks, since those take multiple people to bring down. The general population takes care of the smaller prey."

"And you're a member of the guard, I take it?"

"Youngest member in one hundred and fifty years," Marius said proudly.

"Congratulations," Harry said, smiling at Marius' obvious pride.

"As for why we're here now, we're hoping you can help us answer that," Iulia said.

"How can I answer that for you?" asked Harry. He hadn't even known of their existence until ten minutes ago.

"When Dad recalled all of the Guard members still stationed Above, he didn't completely give up. There are still wizards living here who are loyal to him because they have relatives living in Lyonesse that didn't completely sever all contact when Mers moved Below. So, Dad used a borderline illegal ritual that harvested your magical signature from your favorite blanket and imbued two stones with the signature. One stone was a beacon and was left with a family Above, while he took the tracking stone Below. The beacon was supposed to glow if it detected any magic cast with your signature in the UK. If it glowed, it would cause the tracking stone to glow as well, and both stones could then be used to pinpoint your location," Iulia explained. She reached into her pocket and drew out a perfectly round stone. A green light was emanating from within, gently pulsing every now and then.

Harry took the stone from her and turned it over in his hands. The moment he touched it, the light stopped pulsing and the stone grew warm.

"Dad put his stone in the Grand Hall. Guards are posted there twenty four hours a day, so if it ever glowed, someone was bound to see it, "Iulia went on. "It stayed dull as the years went on. Every year on your birthday, the six of us spent the day in the Hall and just talked about you the whole time," Iulia gave a broken laugh.

Marius held out his hand and Iulia took it, squeezing hard. Harry's heart broke, knowing that his absence had caused so many people so much pain made him immeasurably sad. Then and there, he swore to himself that he would find the person responsible and make them pay.

Marius took over the tale, still holding Iulia's hand. "I was on duty when it happened. The stone, the one you're holding now, rattled and fell off the pedestal, glowing so bright my mum saw it from her house. None of us moved for a good minute, we were all too stunned. Then there was a scramble to get the stone and find King Callum. Alder Fawcett, the one with the other stone, contacted Cal to tell him that his stone had also gone crazy."

Harry was pretty sure there was a Fawcett in his year, but he'd never interacted with the kid. Pushing that aside, he focused on the stone in his hand.

"When did this happen?" he asked.

"June eighteenth," Iulia said.

Harry clenched the stone in his hand so hard, it started cutting into his palm. Ignoring the pain, he pushed on.

"That was the day I fought Lord Voldemort."

Iulia's grip on Marius' hand tightened drastically and he yelped, yanking his hand back and nursing it. "Watch it," he complained.

"You fought Voldemort?!" Iulia yelped.

"It wasn't strictly a fight, he possessed me and I pushed him out. I'm told there was a visible burst of magic that came from me when I expelled him, but I didn't see it." Harry told them.

"That would've done it," Marius agreed. "Anyway, King Callum put together a bunch of scouting missions and we gradually narrowed down your location to this house," he waved toward number four.

If that magical outburst caused the stones to suddenly be able to find him, it might have destroyed whatever glamour was hiding his true appearance. Harry wasn't used to the brown hair and light green eyes yet, but evidently there was no going back. Harry was tired of being called a carbon copy of James Potter anyway, so it wasn't too bad.

Something Marcus said caught Harry's attention just then, something about the King.

"Why was the King so involved?" Harry asked.

"You don't — right, of course you don't know," Iulia said ruefully. "King Callum Caius Aurelius is our Dad."

"I'm royalty?" Harry squeaked. Embarrassed, he cleared his throat. "I'm royalty?" he tried again.

"You're the fourth of five kids," Iulia smiled. "I was sent to come get you because I'm the least noticeable and we wanted to keep a low profile. Mum and Dad couldn't come because they didn't want to attract the attention of whoever took you in the first place. We figured no one would pay any attention to a girl travelling with her boyfriend," she scowled at that last part.

"Honey, you wish," Marius laughed.

"Iulia I get, but why you?" Harry asked Marius.

"I'm young enough to pass for Iulia's boyfriend and I've got magical power to spare," Marius shrugged.

"Marcus wanted to come but Dad refused to risk his Heir," Iulia added.

"Marcus?"

"Our oldest brother," she clarified.

"Will you tell me about them? Our family?" Harry asked, desperate for more information.

Iulia smiled sadly at Harry, reaching up to unclasp her locket. She pried the two sides apart with a fingernail and passed it to Harry, trading it for the stone he still held.

"You should have grown up with us, Harry, and I will forever regret that we missed your childhood," she lamented.

Harry looked down at the gold locket in his hands. The body of it was oval and a stylized I was engraved on the front. Turning it over, Harry saw that Iulia had inserted two wizarding pictures.

On the left, two adults were sitting on paired thrones. The female's hair and eyes matched Harry's exactly, and she was holding a baby who was waving his fist sleepily. Her tail was a beautiful dark blue colour and the tip of a tail was poking out from the blanket the baby was wrapped in. The picture was too small for Harry to make out the colour of the baby's tail. The woman was looking at the baby with such a tender expression of love that it made Harry's heart ache. He assumed that this was his mother and himself as a newborn.

Harry turned his attention to the other people in the picture. Next to his mother was a man Harry took to be his father. The man was sitting on his throne proudly, one hand on the armrest of his throne and the other on the shoulder of a small boy who was grinning wildly. His father had black hair that was tied back in the same style as Iulia's, and ice blue eyes that seemed to dance with laughter. His tail was hooked over the edge of his seat, the green scales gleaming.

The boy his father had his hand on looked just like the man, but with dark green eyes. Next to that boy was a younger version of Iulia, who was sporting a purple tail that waved back and forth occasionally. Iulia was holding the hand of a little boy who looked to be around two or three. The boy was waving madly at the camera, his brown hair bouncing up and down. He had blue eyes like the older man, and a fiery red tail, which made for a startling contrast.

In the picture on the right, the adults and Harry were missing, but older versions of the other three kids were lined up with their arms around each other, along with a blonde girl who hadn't been in the other picture.

Harry looked back up to see Iulia trying to hold back tears and Marius fiddling with his hands, looking just as uncomfortable with crying girls as Harry was.

"What are their names?" asked Harry, tracing the outline of the locket.

Iulia got up and dragged her chair next to Harry's. She sat back down and leaned over so she could see the pictures.

"The man right there," she pointed to the picture on the left, "That's Callum Caius Aurelius, the King of Lyonesse and our father. He hates Callum though, so he tells people to call him Cal. The woman next to him is Lucia Sabina Aurelius, the Queen. She's holding you, I think you were around six months old when this was taken. You were born Hadrian Valens Aurelius, by the way."

She moved her finger over to the boy next to Callum. "That's Marcus Seneca Aurelius, firstborn and first in line for the throne. You preferred him if you weren't with Mum or Dad and he absolutely adored you. I'm the next oldest, right there next to him, Iulia Corin Aurelius. I'm holding Trajan's hand, he must be around two here. His full name is Trajan Soren Aurelius, and he's our resident troublemaker."

Iulia moved over to the picture on the right, tapping the face of the blonde girl. "This was after you were taken. Mum and Dad had always planned for us kids to be two to three years apart, but Cassia Tatiana Aurelius was born five years after you were stolen. I think they blamed themselves a bit for your abduction, so they put aside the idea of having more kids and focused on finding you. To this day, I'm not sure if she was an accident or not. She was five in this picture, she's eleven now."

Iulia sat back in her chair, letting Harry look his fill. "Like Dad, Cassia hates her full name and prefers to be called Cass," she laughed. "She helped us to heal, but no one could ever replace you. She's grown up seeing pictures of you and hearing our stories about you. She's very excited to meet her big brother."

"She won't shut up about it, you mean," Marius corrected. "She's a bundle of energy, that one."

"She is," Iulia agreed.

Harry mourned for the life he could have had. Parents and siblings were all he'd ever wanted, and now two living parents and four sisters and brothers had dropped into his lap. Harry gently closed the sides and gave the locket back to Iulia, who clasped it back around her neck.

"When do we leave?" Harry asked.

"You want to go back with us?" Iulia questioned.

"Isn't that why you're here?" Harry replied, suddenly unsure of himself.

"Yes," Marius said, "But we weren't going to force you to come with us if you didn't want to leave."

"You're both idiots if you think I'm not coming with you after finding out I've got a family," Harry declared.

Iulia grinned widely, looking extremely relieved. "In that case, we'll be leaving on your birthday. We could tell through the tracking stone that your Mer form was suppressed. We don't know how, or why, but we're hoping that the magical boost you get when you come of age will break it and let you transform."

"That's today, though," Harry said, confused. "And I'm not coming of age, I'm turning sixteen."

"Today's not your birthday," Iulia scoffed, "Who told you it was?"

"I —" Harry frowned. He remembered Aunt Petunia telling him July thirty-first was his birthday, but he didn't know if Lily Potter or someone else had told her that.

"I don't know, but you're saying my birthday isn't July thirty-first?"

"No, you were born August tenth! You'll be seventeen in ten days," Iulia told him.

Harry's head spun. Not only had he been celebrating his birthday on the wrong day, he was a full year older than he thought he was.

Born as the seventh month dies…

What did this mean for the prophecy?

Harry didn't know, and he didn't want to consider it just then. He was still wrapping his mind around being the prince of an underwater city.

"So I'll come of age, the boost in the magic will break the binding on my Mer form, then we'll go back to Lyonesse. That's the plan?"

Marius nodded. "Pretty much. We just have to keep a low profile. Alder gave us enough money to rent a Muggle hotel room for the three of us."

"What happens if coming of age doesn't let me transform?" asked Harry. It seemed like a distinct possibility.

"We'll figure it out, don't worry. We're getting you back to Lyonesse one way or another," Iulia said firmly.

Harry nodded, comforted by Iulia's confidence.

"Well," Harry stood up, "I guess I'd better go pack."

Character Bios

Alder Fawcett
Age: 47
Birthday: October 17, 1948
Appearance: Dark brown hair, brown eyes, average height, usually dresses in formal robes.
Alder is the royal family's main contact with the Above. He was in possession of the beacon stone that was linked to Harry Potter until it went off. Alder holds a not-so-secret torch for Cal.

Callum (Cal) Caius Aurelius
Age: 41
Birthday: March 21, 1955
Appearance: Black hair, ice blue eyes, green tail.
Harry's father and King of Lyonesse. Benevolent King, good sense of humour. Weapon of choice is a spear. Took over from his father at 20 after his unexpected death.

Lucia Sabina Aurelius
Age: 41
Birthday: November 13, 1954
Appearance: Light brown hair, bright green eyes, dark blue tail.
Harry's mother and Queen of Lyonesse. She is a strong advocate for justice and likes to emphasize the importance of being kind. Very talented with a variety of musical instruments.

Marcus Seneca Aurelius
Age: 22
Birthday: September 24, 1972
Appearance: Black hair, dark green eyes, green tail.
Harry's oldest brother and Heir apparent. As a child, he was very carefree, but the loss of Harry turned him into a very serious child. Marcus is very dedicated to his studies and is determined to make his parents proud.

Iulia Corin Aurelius
Age: 21
Birthday: January 7, 1975.
Appearance: Black hair, dark blue eyes, purple tail.
Harry's older sister. Iulia was chosen to retrieve Harry after the Guard and Alder pinpointed his location. She is very headstrong and will disobey orders if she thinks she has a better way of doing things. She prefers verbal sparring but can and will wipe the floor with her opponents.

Trajan Soren Aurelius
Age:19
Birthday: April 30, 1977
Appearance: Light brown hair, ice blue eyes, red tail.
Harry's second oldest brother. Trajan takes pleasure in pranks and general mischief and mayhem. Not very studious but bright in his own way. Very loyal and prone to getting into fights to defend someone else's honor.

Hadrian (Harry) Valens Aurelius
Age: 17
Birthday: August 10, 1979
Appearance: Light brown hair, bright green eyes, purple tail.
The Harry we all know and love, just with a tail. He is more suspicious of Dumbledore than in canon and also less attached to Ron and Hermione.

Cassia (Cass) Tatiana Aurelius
Age: 11
Birthday: February 16, 1985
Appearance: Blonde hair, dark green eyes, dark blue tail.
As the youngest of five, Cassia is somewhat spoiled. Everyone is very protective of her since she was born after Harry's abduction rattled the city. She is very energetic and keeps everyone on their toes.

Marius Marcellus Mercator
Age: 18
Birthday: March 9, 1978.
Appearance: Light brown hair, brown eyes, silver tail.
Youngest member of the Guard in 150 years, and will tell anyone who listens about it. Very proficient with a variety of weapons. Oldest of three kids. He takes his duty seriously, but has a good sense of humour. His family is close with the royal family and Marius is good friends with Iulia and Trajan.

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