Summary: Merlin is curious about the legend of a mysterious mermaid, so asks her guardian, the goddess Elizabeth, to take her to investigate the truth.

A/N: Welcome to another oneshot! This was my second entry for the latest Sin Swap over on Tumblr. I was partnered with the amazing user mercurialvoid, who drew a picture of Elizabeth as a mermaid in a bottle that positively captured my imagination. From that picture, my job was to create a fan work of the fan work, and this oneshot is the result!

I'd like to thank mercurialvoid deeply for creating such an inspiring picture, and allowing me to use it as the cover art for this story. Please go check out the rest of this amazing artist's work on Tumblr!

War had come to Britannia.

A clash here and there between the demons and the goddesses had escalated in hostility until it had spilled over to the other races. Both clans were determined to rid the world of one another, seeing the other as a threat to their very existence. The demons had chosen to use the remaining clans as pawns to force the goddesses to relent, but that had backfired; now the giants and fairies aligned with their enemy. It was an all-out war.

In the midst of the battles and blood and loss, the screams and the battle cries and the sounds of metal scraping, the ruined towns and piles of bodies and demon fire that could not be quenched, two girls sat together, braiding each other's hair and chatting and enjoying the late summer morning.

The goddesses had a stronghold in Britannia that was heavily guarded, and always occupied at least one of the Queen's Archangels. There the Queen's daughter Elizabeth would find solace from the pressures of the war and the expectations of her mother.

There, Elizabeth would also find her little charge, Merlin. The girl prattled on about a book she had been reading, and the goddess sighed to herself as Merlin pulled her hair into a knotted twist. She and Meliodas had travelled to Belialuin to speak to the master there in hopes of having him join their alliance. Yet when they arrived, they found the place destroyed, its people gone, and only a little girl left in the wreckage.

Merlin had proven to be an incredibly talkative and inquisitive girl who demanded to know everything and would not take no for an answer. Meliodas had muttered something about leaving her there—after all, the girl had somehow survived the carnage and living on her own afterwards—but Elizabeth wouldn't hear of it. Since she was not a goddess, Merlin could not go to the Celestial Realm, so Elizabeth had her safely settled in their stronghold under her personal protection.

"Can we go swimming, Sissy?" the girl asked suddenly.

"Hmmm." Elizabeth glanced out the window to the overcast sky. "It's a bit chilly today to go swimming. What about—"

"But I want to!" Merlin insisted. "There's something I need to do."

Elizabeth turned and looked over her shoulder, raising an eyebrow slightly. "This isn't one of your investigations, is it?" she asked with a bit of a warning tone.

Merlin smiled innocently. She had recently been forbidden on doing any more experiments without explicit permission. The last one had left a large hole in the wall of the kitchens and one of the cook's assistants with webbed hands and feet. "Of course not!" she piped sweetly. "But I read something I want to look for."

"Oh?" Before Elizabeth could ask anything further, Merlin was scrambling away and running for one of the piles of books that seem to now litter every room of the building. Pulling one out, she quickly returned to sit next to the goddess.

"Here," she said, turning the pages expertly. "I want to find this."

Elizabeth looked to where Merlin's finger pointed. "The Mermaid of Brigan," she read aloud, her brows darting up in surprise. "Mermaids, Merlin?"

The girl looked up at her with a scowl. "They could exist! There are a lot of legends about them, and they can't all be false."

Unable to stop the chuckle that escaped her, Elizabeth asked, "Why do you want to find this one?"

With a grin Merlin assumed the stance she always took when explaining things to grown-ups. "The Mermaid of Brigan lives in pool that is landlocked, but it has salt water. Can you believe it? That's why I think this one must be true. There is no reason for a lake in the middle of Britannia to have salt water unless there is something living in it to make it so."

Elizabeth nodded as she scanned the story. "It is an interesting phenomenon. But there must be some explanation."

"That's why I want to go see." Merlin climbed up next to her and gave her a bit of a pout. "Please Sissy? Please? What if there is a mermaid there? I need to know!"

"It says here the mermaid is only seen at night," Elizabeth read. "So going now would be quite useless."

"Perfect!" Merlin shouted, jumping up and clapping her hands. "We'll go after dinner! Thank you Sissy!"

She turned and ran out the door as Elizabeth shouted, "No, wait-!"

Twelve hours later, Elizabeth stifled a yawn as she walked down a slight hill, watching Merlin skipping ahead in the darkness and listening to a demon grumble beside her. "Why did I have to come along again?" he grunted.

"Because," she answered pleasantly, "these parts are still wild, and we don't know what we'll find here."

"If there isn't a mermaid in this pool I'm going to drown her in it."

With a snort Elizabeth scolded, "Don't be such a spoil sport. You're making a young girl happy. Isn't that important?"

"I'd rather make you happy." A hand snaked around her hip and grabbed her rear, nearly lifting her off the ground, and Elizabeth shrieked out a laugh.

"Quiet!" Merlin hissed, turning to face them with her hands on her hips. "You'll scare the mermaid!"

The demon muttered a few choice words under his breath, but released his hand on the goddess all the same. "How exactly do you scare a mermaid?" he snorted, walking ahead to catch up with the scowling girl.

He reached out to pull her hair, but Merlin swatted him away. Elizabeth chuckled to herself as they resumed walking: only this girl would be bold enough to smack the hand of the most fearsome demon in Britannia. "She could be frightened of people who would use her power," Merlin whispered to him.

"What power?" he asked suspiciously.

Elizabeth covered a laugh as she watched Merlin draw herself up to lecture her companion. "The mermaid has healing powers, and I think that is what causes the salt in the water. And if she finds you pleasing, she can even grant immortality."

"What if she doesn't find you pleasing?"

Merlin's smile turned mischievous. "She pulls you under the water until you drown."

"Oh really?" he teased. "And what are you planning to do if she's there?"

"Catch her and put her in a bottle," answered Merlin pointedly.

The demon's laughter erupted in the quiet. Merlin protested, grabbing onto his arm to give him a shake, and the two continued to squabble the rest of the walk to the pool.

When they arrived, the moon was overhead, the light reflecting off the shimmering surface. Merlin eagerly took off in a run, scrambling down the side of the hill to reach the water. There was nothing else there, mermaids or otherwise, but the girl began unpacking her bag and laying out her things to prepare for catching the mermaid.

Elizabeth found a spot nearby to sit and watch. She sat on a large boulder, her legs tucked neatly underneath her, shaking her wings out for a moment to stretch. A second later the demon joined her, sitting beside her with one foot planted as the other hung below.

"There are no damn mermaids here," he said to her quietly.

"I know," Elizabeth sighed. "But it makes her happy, so what is the harm?"

"Filling her head with ideas," he answered. "As if the answer to anything is as easy as catching a mermaid in a bottle."

Elizabeth looked at him with a frown. "Meliodas?" she whispered. "What's wrong?"

For a while he did not speak. They simply watched as Merlin took samples of the water, consulting a book every so often for reference. The girl was becoming adept at magic, and had created a little ball of soft light to see by. "Summer is nearly over," he said finally. "The war will only get harder as it gets colder."

Elizabeth murmured her agreement. "We are doing all we can. There is nothing more to do than that." She glanced back at him and asked softly, "Have you spoken to any of them?"

"Zeldris is the king's executioner now," he answered. "I could not speak to him. It would be too dangerous. One of us would have to die."

The goddess swallowed nervously at the thought. "And Estarossa?" she whispered. "Have you tried to reach him?"

The dark silence that came from the demon served as her answer. Not wanting to press any more, she turned back to watch Merlin as she waited by the pool. But she reached out and slid her hand over his, and to her relief, he allowed it, even weaving his fingers through hers.

An hour later, Merlin walked over to where they sat in companionable silence. "I don't think she's coming," she pouted.

"Giving up so soon?" Meliodas chuckled. "What about your wishes?"

Merlin sighed loudly. "I guess I'll have to find some other way of becoming immortal."

"Immortal!" Elizabeth exclaimed. "Why on earth would you want to be immortal?"

The girl laughed at her dismissively. "How else am I to learn everything about the universe, Sissy? If I die before I know everything I'll be very upset."

"It's probably for the best," the goddess said gently. "It would be very cruel to take the mermaid from her home to live in a bottle on your shelf."

"What did the mermaid look like anyway?" Meliodas asked.

"I'm not sure," admitted Merlin. "But I drew a picture, do you want to see?" Without waiting for an answer she scurried back to her pack, pulling out another book with papers stuffed inside. Almost reverently she carried it back, carefully handing it to Elizabeth. "Careful, Sissy. This has all my notes inside on everything."

"I see," she answered, leafing through the pages. Some had writing, some had incredibly long math equations, some had what looked liked recipes—for what, Elizabeth was scared to know. Others had sketches of machines of all kinds, her "inventions" she assumed. There were even more pictures, drawings of animals with labeled parts, maps, landscapes, people… and some rather disturbing ones that she made a mental note to discuss with the girl later.

On the last page was a beautifully illustrated drawing of a glass bottle, filled nearly to the top with water. Inside was a mermaid who had a dark fin with blue markings, pink shells, and familiar silver hair flowing around her.

"This looks like Elizabeth," Meliodas chimed in as he peered at the picture.

"Of course," Merlin answered. The goddess felt her cheeks burn a bit as she stared at the drawing. "Mermaids are beautiful, and since Sissy is the most beautiful person in the world, I figured the mermaid would look like her."

Elizabeth looked up at the girl, her eyes soft as a smile broke on her face. "What a sweet thing to say," she beamed.

She heard Meliodas laugh next to her, a sound that she did not hear often, and it made her blush even more. But Merlin was already pulling the book from her hands, chiding them both, "Well come on, we don't have all night. I need to get these water samples back to my lab. If there is no mermaid, there must be some reason the lake is salty."

Meliodas followed Merlin back, and Elizabeth watched as he crouched by the water, talking to the girl as she packed up her things. For a moment Elizabeth wondered if they would ever get a chance like this again, that there would be another night where they could go exploring with Merlin or walk through Britannia without trouble coming along. If they would have another time to try to find a mermaid or a sprite or a talking tree or whatever else the girl would read about in a story. If they would ever have peace.

"Come on Sissy!" Merlin called, waving her over, and Elizabeth smiled and stood. They would have another moment, they would have peace, and she would make sure it happened, one way or another.