“When you have reached your fifteenth year,” said the grand-mother, “you will have permission to rise up out of the sea, to sit on the rocks in the moonlight, while the great ships are sailing by; and then you will see both forests and towns.”
--"The Little Mermaid" by Hans Christian Andersen (1836)
When Byleth breached the surface for the first time, it was to a black sky and a gibbous moon, blue-tinted and bright. The way moonlight reflected on the surface of the water was different, seen from the surface; sharp shards of light twinkling like stars on the waves.
She watched for a short while, eyes tracing the vast emptiness between the sky and the surface of the sea, and then slipped under the water again. But she did not go back to the depths again, instead skimming along the surface.
There was a ship nearby. She had seen its like many times before--the bellies of these vast wooden beasts that the surface-dwellers rode across the oceans--but she had never had reason to approach. She still did not have reason, exactly, but it was her birthday and she was allowed to see the surface, and this was what she wished to see. This time, when she came to the surface again, she was near enough to the light coming off the ship: unlike the moonlight, it was oily yellow on the waves, stretching in long swathes away from the ship. A warm din of music and merriment washed off the ship, indistinct but loud enough to rise above the sound of lapping waves.
But Byleth kept in mind all of her father's advice about staying out of sight. She swam under the touch of the yellow light, where the humans might spot her if she surfaced, and weaved under and around the ship as she assessed the best angles of approach.
They hadn't had a war against the humans in a terribly long time, and her father didn't seem to think there was a chance of it anytime soon, either, but there was no harm in seeing the capabilities of the other side up close. There was only so much Byleth could learn from old algae-parchments and tales from before her birth. Even Jeralt, cautious as he was with her safety, had rubbed his chin thoughtfully and opined that maybe, given how quickly things changed on the surface, it would do her good to see some things up close.
Some things, Jeralt had said pointedly, before instructing her to return as quickly as possible at the slightest sign of trouble.
But now that she was here--well, it was not that Byleth felt incautious. It was only that she felt there was not much she could learn only by running a hand against the dead wood that made up the ship's hull. It was not like the ship itself was a living creature, and the humans now distracted by their celebration, and the night being so dark, this was as good opportunity as she was going to get to observe without anyone observing her in turn.
That being said, the heavy chain of the anchor had links so large that they made for good handholds, and Byleth judged that even with the strange press of gravity and a lack of legs, she would still have little difficulty climbing up and getting a closer look at the deck of the ship.
The drawback to having a celebration on a ship, Dimitri discovered, was that one was fenced in by the sea on all sides, and unable to escape unless one proved willing to swim all the way back to shore.
Less generously, Dimitri thought that was precisely the reason his friends had proposed this event be at sea. They had finally figured out a way to stop him from slipping away from the festivities halfway through.
Not that this stopped him from getting some distance anyway. The ship was overflowing with guests, and their cups were overflowing with wine, and the music played them into good cheer and dancing all night, but Dimitri found himself above deck, slipping into the shadows. The music could still be heard, and so loudly that Dimitri felt it like a thrum in the soles of his feet, but the night was cool, and the sea breeze was gentle on his face. Out here, he could breathe.
And apparently he was not the only one with this notion. He had walked nearly right up to her before he even noticed the woman sitting down between two posts of the railing, her legs dangling over the edge of the ship and into the darkness. In the interplay of light and shadows coming from the closest cabin window and farther-placed lamps, he had not noticed her until she'd turned her head, and the seashells braided into her seafoam-colored hair made delicate clinks in the darkness.
"Oh! My apologies!" Dimitri said quickly, feet sticking in place with embarrassment.
Her shoulders tensed. They were bare, and Dimitri almost mistook her for naked before he saw the pale shimmer on her back and torso, of a material that was textured like fishscales. He was unable to identify it in the darkness, and he was also unwilling to stare rudely at a maiden, so he looked off over the railing and onto the placid sea beyond.
"I did not mean to intrude," he said.
"You're... not intruding," she replied, not turning towards him. The fall of her hair concealed most of her face, so that he saw only the suggestion of a cheek, the tilt of a chin--the twist of a smile at the corner of her mouth. "I was only... I was sitting here, listening to the music."
"Would you mind if I joined you?" he asked.
"Ah... you..." She ducked her face away for a moment, turning it into the shadows. "You may sit there," she said finally, gesturing towards the deck, away from the edge--and from her.
"Thank you," Dimitri still said graciously, sitting down cross-legged. "But... please, do not sit so closely to the edge. If you fall, I fear nobody would even hear the splash."
She half-turned towards him, then. Enough for him to see the flash of eyes as pale as her hair, and an incredulous expression, before she looked away again.
"I can swim," she said so curtly, that Dimitri almost thought he might have offered insult.
"Of course," he said, for lack of anything better.
They lapsed into silence for a while. The music continued to play. Dimitri looked away, and sensed the woman's tension ease when he did so.
"Are you enjoying the celebration so far?" she asked after a while, jarring Dimitri out of his thoughts.
"I-- well," Dimitri tripped on his own tongue as he tried to produce an answer both diplomatic and truthful, "I fear I'm not good at enjoying these things."
"Then why participate?" the woman continued her inquiries.
This gave Dimitri pause, because he would have thought it self-evident. He was the prince, and this was a celebration of his upcoming coronation as king. He could hardly refuse to be present. But then he realized the young lady had perhaps not gotten a good look at him either, in the semi-obscurity of this spot, and him with light at his back, and so she most likely did not realize who he was. It gave him a feeling like relief, this small measure of anonymity he had accidentally managed to gain.
"I am here at the behest of friends," he chose to answer, which was at least a partial truth. "And I'm always pleased to see them enjoying themselves. What about you?"
"Me?" She sounded surprised by the question. "I've never been to something like this before."
Ah, probably one of the younger daughters of nobility. Dimitri couldn't place her, but if she had only recently been introduced at court, he probably hadn't had time to learn her face yet. It was probably unwise to sit our here with her without a chaperone, if she was one of the usual young ladies whose mothers were constantly pushing them onto him with designs on marriage.
But she seemed so disinterested in court politics and so content in her spot, that he was loathe to bring more people into it. And he was too tired to bear the presence of too many individuals at the moment. So he kept his peace, and she kept hers, and they enjoyed halting fits of conversation as they continued to sit together.
She liked the music, but not when it was too loud; she eluded any questions on genre when he tried to pose them to her.
He told her about his friends, and why they were dear to him, and almost feared she would recognize who he was by the names, but she had no reaction to it.
She told him, vaguely, of an overprotective father, which was not surprising for a young woman of such arresting beauty as Dimitri could only guess by what little he could see of her. But she did not give him any clues as to who her father might be.
And then, she looked to the sky, and sighed.
"I'll have to leave soon. There's a storm coming," she said, sounding regretful.
But Dimitri looked to the sky, and saw only the moon, nestled among placid white clouds. No winds, and no black gathering of thunderclouds at the horizon.
"Can you smell it, like the sailors can?" Dimitri asked.
"Smell it?" she repeated, baffled. He couldn't blame her, Dimitri had also thought he was being the butt of a joke when he'd first been told something like that. "I... suppose," she said more cautiously. "It's more like I'm tasting it."
"Like merfolk," Dimitri blurted out, and she flinched.
"Pardon, it's a story my father would tell me when I was younger. That merfolk could taste seastorms before they arrived, and then drink them for power."
The woman remained quiet in the wake of this information, and Dimitri felt awkward now.
"It's foolish, I know," he admitted with a nervous chuckle. "Nobody had even seen merfolk in generations. In truth, it seems more like myth than history--"
He cut off at the sound of heavy footfalls against the deck, because he recognized them. He rose to his feet as Dedue came around a corner and stopped there to peer into the darkness.
"Your Highness," Dedue's low voice called out.
"Dedue! I take it I'm being missed," Dimitri said.
"They are asking for you," Dedue confirmed.
"Of course. One moment, I have--" Dimitri turned to say his goodbye to the woman, but as he turned and looked to her spot, she was gone. Confused and not a little bit alarmed, he peered over the railing as well, but there was no splashing in the water, and no sign at all that someone had fallen in.
He took a longer look down the length of the deck, as much as he could see, but he could not see hide nor hair of the young lady, for all that you would think hair that color would be easy to spot even in the darkness.
"Your Highness?" Dedue spoke again.
"Nothing, Dedue. I'm coming," Dimitri said, eyes scanning his surroundings one final time before he followed.
Perhaps he would spot her below decks. The celebrations would continue for a while yet. He had time to look.
The merriment on the ship continued on, even as the storm that Byleth had predicted began crowding the horizon. She did not dare climb onto the deck of the ship again, when she had come so close to being found out, but she followed even as the ship raised anchor and began sailing away.
It was time to go back down, to the depths where merfolk lived, but something about the taste of the incoming storm felt slightly off to Byleth. It felt like smoke at the back of her throat, like something--not necessarily bad, but manufactured. It wasn't until she recognized it as the taste of dark magic that she thought to look, but when she did, it was easy for her to spot the easy glide of ships over the seas.
She sank down, and looked up towards the outlines of the ship skimming across the surface of the sea. The dark clouds had eaten up that blue-tinted moon, but she didn't need the light to see underwater. She could see the bellies of the ships as clearly as she could see anything in the depths that light had never touched.
She watched curiously at first, trying to figure out why the three new ships were circling like predators around the celebration vessel, and then she understood just as the ship began sinking.