A/N:

mostly canon-compliant

ideal formatting is on ao3 (link in my profile). i post the new chapters there first.

i would be most grateful for any reviews/thoughts. enjoy! :)

1180

Blue Sea Moon

The assassination plot Catherine discovered during their last mission sent the monastery into high alert.

Classes and trainings were reduced so all professors and students could patrol the grounds and set up defences against any possible attempts on Lady Rhea's life. Many students took to their new tasks with fervour, reporting punctually for their patrols and checking every nook and cranny of the monastery for secret entryways and passages. Ferdinand was convinced the plotters would set fire to the stables as a distraction and could frequently be found standing guard over the horses in the stables; while Petra stole away daily to set traps in the woods explaining they could at least have food even if "they do not catch the bad people!"

Edelgard and Hubert, however, were of a different opinion.

A distraction, they believed—the true target of the plotters somewhere or something else in the monastery—and had launched their own investigation, for which Edelgard asked Byleth for assistance. So, on top of her extra tasks and patrols, Byleth found herself swept up in the questioning of monastery inhabitants as well.

It was a marvel how her life had changed.

One day she was a humble mercenary, and the next, she was eating cake as part of an information gathering quest.

"How inconvenient," Lysithea said, shovelling said cake—raspberry and cream—into her mouth. "With everyone stuck on guard duty, our study and training is much reduced. I do not have time to waste!"

"Some things are more important than studying and training," Byleth said, eating her cake at a much more leisurely pace.

"I understand. But it doesn't change the fact that it's a royal pain. I need to work hard to become stronger."

"You always seem to be pushing yourself, Lysithea. It's okay to take a break every now and then."

Lysithea brows knitted together in consternation, then she looked down at her cake, chewing furiously while she thought. "Hmph," she said when she'd finished her bite. "You don't understand, Professor."

"What don't I understand?"

"Never mind. You should pay more attention to people. You didn't know I was younger than everyone else. And you've never once asked why my hair is white."

"I…" Byleth trailed off, confused at the abrupt change in conversation.

"And since you're only interested in what I think the real target of the plot could be, my opinion is that it's the Holy Mausoleum. The day of the Goddess' Rite of Rebirth Ritual is the one day the Mausoleum is open to the public."

Byleth stared at her. "How did you know that's what I was interested in?"

"You've asked countless people about this in the past fortnight. I, unlike you, pay attention."

"I pay attention," she replied defensively. "I've just never thought about… your hair colour."

"Exactly. Clearly you do not pay enough attention."

Byleth frowned. She wasn't sure how a simple questioning exercise had ended up with her being criticised, but in the short time she'd known Lysithea, she'd found the student to be intelligent and sharp in tongue, her feisty quips often disconcerting many others. But like Edelgard, Byleth felt there was something more underneath the front that Lysithea portrayed; that she somehow seemed like both a mature adult and an immature child at the same time.

But that was not a matter for that evening. She finished her cake and stood, eager to share what she had learnt with Edelgard. "Thank you, Lysithea. You have been very helpful."

"Wait, Professor!" Lysithea cried and hurriedly shoved the rest of the cake into her mouth. "Yumfh– bemfh—" she swallowed, an abashed look replacing her earlier fractiousness. "You're beginning patrols right? I think you should patrol back to the dormitories. Intruders could be hiding there, you know?"

Byleth raised a brow. "Right… intruders… Not because it's dark outside and you, who are afraid of ghosts, have to walk alone back to the dormitories for curfew?"

Lysithea looked affronted, bringing a hand to her chest. "What?" She scoffed. "Of course not! I was simply proposing a mutually beneficial plan of action. You have to patrol. Intruders could be at the dormitories. If we walk back together, I could help you if there are intruders. It's a total coincidence that it's nighttime and when ghosts come out to play."

"I see." Byleth couldn't help but smile. "Well, since you've been so helpful… let's go."

Lysithea hopped out of her seat, failing to hide the relieved grin on her face. And as they proceeded on this apparently mutually beneficial plan of action, Lysithea launched into a lecture about the different types of ghosts that could exist in the world, only stopping when they reached the dormitories.

"Lysithea," Byleth said before Lysithea went into her room. "If you would like to do more training, you could join my class for the month. We will be heading to subdue bandits nearby this weekend, and I still make time for lessons."

Lysithea looked thoughtfully up at her. "But you're not good with magic. Why should I join you?"

The headstrong girl never failed to amuse her. "Just an option," Byleth said gently. "A good mage must know more than just spells. They must learn teamwork; know battle strategies and positions to gain the best possible chance to strike; build stamina and resistance to defend against even the strongest of warriors. These are all things you can learn with me."

"You think rather highly of yourself, don't you? For someone who doesn't pay attention."

Byleth chuckled. "Again, just an option."

"Hmm. I will consider it."

"Alright. Goodnight, Lysithea."

"Bye, Professor." Lysithea shut the door loudly in her face and she heard the lock click in place.

Byleth didn't think locks would do much against ghosts, but that was not a battle she wanted to fight with Lysithea. And so, she shook her head, then went to begin her real patrols.

The next morning, Byleth was looking over her lesson plans for the day when a commotion from the students drew her attention.

"Lysithea! Welcome!" Caspar boomed. "Are you joining our class this month too?" He pointed at Mercedes, who sat beside him. "Mercedes is here as well!"

"How wonderful!" Ferdinand said before Lysithea could respond. "With Ordelia on the border of our countries, it is of paramount importance we maintain a healthy relationship!"

Lysithea stood unmoving at the entrance of the classroom, back nearly arching like a cornered cat at the attention. "I'm just joining for the month! And only because the Professor begged me to."

The Black Eagles and Mercedes all swerved their heads to her.

"I did not beg," Byleth said lightly. "But you are most welcome to join us for the month." She gestured to an empty seat beside Petra.

"It is so nice to be having someone the same living years—oh, age—as me in the class!" Petra said, beaming at Lysithea as she sat.

"And one who enjoys sweet things too," Mercedes added, placing a cupcake in front of Lysithea, making her eyes widen. "Freshly baked this morning."

"Oh, Mercedes! Thank you!"

"Finally," Linhardt chimed in. "Some more brains in this classroom."

"Excuse me?" Dorothea gasped.

While the Black Eagles bickered, Edelgard came up to Byleth's desk. She looked particularly tired that morning—dark shadows under her eyes, a lock of hair loose from her ribbon. She wondered if Edelgard had suffered nightmares the night before or whether she was exhausted from her investigations. Unlike the month prior, Byleth had barely spent any time with Edelgard in recent weeks. Since the discovery of the plot, Edelgard and Hubert were often nowhere to be found; and on times she spotted the princess in the monastery, she was deep in discussion with Hubert or writing letter after letter, no doubt in correspondence with her own sources for the investigation.

"Professor," Edelgard said quietly. "Lysithea is an excellent student. Driven and prodigious. But she is frail. Our missions this month are likely to be dangerous. I would not wish for her to come to unnecessary harm."

"All the better for her to learn from us," Byleth replied, looking over to Lysithea, who was currently being interrogated by Hubert for any ulterior motives for joining their class, Dorothea behind him looking like she could strangle him for his ill manners. "We have several magic users with varying levels of strength, defence, resistance, and skill in both dark and white magic. Lysithea, with her tenacity and prodigious abilities for both types of magic, has great potential as a gremory. She will do well to learn from them in her areas of weaknesses and them from her, in return."

Edelgard listened without interrupting. Then, she nodded. "It seems you are more thoughtful than I gave you credit for. Apologies, my teacher." A soft smile lightened her face, warmed Byleth's chest. "I will, once again, trust in your judgement."

Byleth nodded. "And besides, she discerned the likely true target of the plot."

"Oh?"

"The Holy Mausoleum."

A glint in Edelgard's eyes. "Ah, of course. Most excellent indeed."

As Byleth expected, Lysithea fit into the class like a glove.

She took well to Byleth's strategies and commands and did her best to keep up in fitness exercises alongside the physical fighters. From the mages in the class, she learnt from their strengths—Hubert's cunning and stamina; Linhardt's intelligence and efficiency; Mercedes' optimism and consideration; Dorothea's creativity and agility. And simultaneously, they learnt from her—Lysithea forced Hubert to think outside of his calculating schemes and face the enemy head on; Linhardt to work harder and push himself; Dorothea to learn more spells and build her magic proficiency; and Mercedes… well, to bake more sweet treats to satiate Lysithea's seemingly insatiable sweet tooth.

Most of all, Lysithea was powerful.

She may have been frail, but she made up for it in pure magical strength and comprehensive knowledge of spells. With her assistance, the Black Eagles coasted through their tasks and side battles easily that month, subduing bandits and setting up defences.

And her power was never more appreciated than on the day of the Goddess' Rite of Rebirth.

Lysithea was right. The true target of the plotters—Western Church soldiers—was the Holy Mausoleum. Thanks to their preparations, the Black Eagles were not too far behind and advanced quickly to try and stop them from opening the casket of Saint Seiros. With coordination borne from countless hours of training and real missions, they swept through the priests easily, making good ground until a new enemy stood in their way.

A Knight, sat on his horse wearing midnight black armour and a mask of a skull with curved horns. He stared at Byleth with flaming red eyes as the priest she had just slew collapsed to the ground in front of her.

"Like moths to a flame," he said, voice strangely muffled and echoey.

"Who are you?" she asked.

The Knight did not move, only watched her carefully. "I am the Death Knight," he replied.

Byleth saw the mages at the casket behind the Death Knight grow excited; they must nearly be done with breaking the seal. She gripped her sword tightly. The Black Eagles were somewhere around her, locked into their own battles. It was up to her.

"Surrender," she ordered.

The derisive laugh the Knight emitted was tinny, cut short when Byleth rushed him, springing into the air to slice off his head. His lance came up quickly to parry and she dropped to the ground, whirling rapidly into another blow that he also managed to block. Then it was his turn, and he bore down on her with a vengeance that felt personal in its savagery.

Byleth swung just in time to meet his lance, his strength nearly dropping her to her knees. But Edelgard was suddenly by her side, and together they pushed the Death Knight back, his horse rearing up. Without a care for her safety, she stepped in front of Byleth and shouted, "No! You cannot kill her!"

Byleth's stomach dropped.

The Knight paused for the barest of a second.

But before he could raise his lance, before Byleth could move to protect Edelgard, dark spikes materialised all around him, then pierced his armour and the ground with lightning speed, forcing him back and his horse to rear up again with a whinny. And in that time, a fierce protectiveness drove Byleth to shove Edelgard behind her so she was shielding her from the Death Knight.

Red pinprick eyes flared with hatred. "I didn't expect to encounter someone like you… how unfortunate," he snarled at Lysithea, who had run up to support Byleth and Edelgard, panting heavily. Ferdinand and Caspar were close on her heels, keeping her safe from other melee attackers. The Death Knight looked back at Byleth. "I will kill you next time," he vowed, then disappeared into thin air.

"Stop being so weak!" Lysithea cried at them. Grime and sweat matted her hair and face. "I can't save you every time, you know!"

Despite the chaos raging around them, Byleth and Edelgard exchanged an amused glance.

"I think she's talking about you?" Byleth said teasingly at Edelgard, making her scoff and throw her cape back over her shoulder haughtily.

"As if. I am confident she's talking about you."

"I'm talking about you two!" Lysithea shouted angrily. "Ugh!" She flung a dark ball of venomous gas at the dark mage that was creeping towards them. It knocked him off his feet, blood spraying from his mouth. "Pay attention!"

"Thank you, Lysithea. Well done," Byleth said. Then, face hardening, she whipped into action and took two other priests down before they could launch any attacks. Edelgard was not far behind, limbs and torsos and innards scattering around in her wake. The way forward finally clear, they charged towards the mysterious mage at Saint Seiros' tomb.

What happened next would haunt Byleth for weeks.

One moment the mage was pulling out a sword from the tomb to swing it at her, and the next, it was in her hands, thrumming with power and energy. Sothis gasped in recognition in her mind, a sense of familiarity radiating through every nerve in Byleth's body. When magic crackled in the mage's hands, she acted without thinking—she swung the sword like it was a natural extension of her, and it whipped out in a clean strike to decapitate the priest.

His head thunked onto the ground.

All stared at her, at the relic hidden in Saint Seiros' tomb for centuries. Alive in her hands.

Even Lysithea could muster no witty repartee.

The nightmares returned in earnest.

For a short while, her nightmares were replaced with fleeting dreams of lilac eyes and a soft smile. But in the nights since the Goddess' Rite of Rebirth, there had been no respite. Each night she saw the woman and the man fight, the man wielding a sword with a unique and impossible whip-like action she'd always attributed to the fantasy of dreams, but now knew was real.

She had held the sword herself.

That night was no different, she snapped awake, gasping for breath, feeling at her intact chest and stomach. But she was unhurt. She was not on a battlefield. She was in bed. In the monastery.

She looked at the clock. Four in the morning.

She wouldn't get any more sleep that night. Especially after what Hanneman told her that morning.

Wrapping a cloak around her body, she headed to the fish pond for fresh air. There, she sat with her feet dangling over the water and simply breathed. One deep breath in. One deep breath out. Soon, she relaxed, body and mind calm once more. Jeralt had always been impressed at her uncanny ability to remain in the present and seemingly emotionless in the most intense of situations.

"My teacher." Edelgard's soft voice broke the silence. The princess was also wrapped in a thick cloak against the cold and her hair was pulled into a low ponytail. Concern creased her face as she studied Byleth. "Is something the matter? It's nearly morning."

"I could ask you the same. It's curfew."

"Well, I…" Edelgard shifted on her feet, clad in simple flat boots. "I had trouble sleeping and I despise being cooped up when that happens. The fresh air helps."

"I understand. I couldn't sleep either. It's been… an eventful few days."

"I'm sure. May I… join you?"

Byleth glanced about. It was the time of the night that was too late and also too early for anyone to be awake. There was only the chill of the air and the half-moon behind the misty clouds as witnesses. So Byleth nodded and Edelgard sat beside her, their shoulders nearly brushing.

"Do you want to talk about it?" Edelgard asked after a while. "Someone wise once told me talking about difficult things with somebody else helps." She smiled, the light breeze fluttering her hair, silver under the moonlight.

Byleth couldn't help a reluctant smile back. "How wise of them indeed."

Edelgard waited, saying nothing.

Perhaps it was the way Edelgard didn't push. Perhaps it was the way the princess looked at her with such compassion it made her feel at ease the way nobody else but Jeralt did. But whatever it was, she felt compelled to speak, to share. "Hanneman told me today that I had the Crest of Flames. A long-lost crest."

When Edelgard said nothing, Byleth glanced at her. "You knew that."

Edelgard nodded. "The Sword of the Creator could only have been wielded by someone with that crest. A descendent of… Nemesis. Even if he'd never been known to have any." She frowned. "Although how you managed to wield it without its crest stone… that's a mystery."

"I see," Byleth said. She looked back to the water, to its stillness, letting it keep her calm. "Remember how I told you I dreamt of a man and woman fighting viciously?"

"Yes."

"In it, the man wields the Sword of the Creator." Byleth avoided Edelgard's startled glance her way. "And… when the woman stabs him to death, I feel the wounds as though they're my own. For so long, I always thought it was just a dream. But… now I wonder if he was Nemesis; whether the woman was Saint Seiros; and for some inexplicable reason my nightmares are his memories… inherited in my blood as his descendent. And with that, perhaps this mysterious ability to use the sword without its stone." She shook her head, sighing heavily. "I know it sounds ridiculous—"

"I don't think it sounds ridiculous," Edelgard said at once, leaning towards her in care. "Crests… they're complicated phenomena. Having mysterious powers and memories intertwined with your crest is not the most far-fetched thing that can be associated with them."

"Thank you, Edelgard." The knot in her chest eased somewhat. She kicked her legs out. "I feel… strange. Unmoored. That there's more to me than I ever thought or cared for. I've never thought too much about who my mother was—Jeralt never spoke of her and I never asked. But I should have wondered more, now knowing she must carry the Crest of Flames."

"Will you talk to Jeralt?"

Byleth nodded. "When he returns from his mission."

"Well, it seems your mother must at least share the same blood as Nemesis. Unless…" Edelgard fell silent for a while, then hesitantly, she asked, "Out of curiosity, have you ever been experimented on as a child?"

"What do you mean "experimented"?"

Edelgard's bare hands tightened into fists in her lap. "I mean imprisoned in a basement and tortured by mages."

Memories flashed in Byleth's mind—a group of children wearing rags, dirty and unwashed, chained to a wall; anger that blotted everything else in her mind; raging flames and the smell of smoke. She forced herself back to the present. "No," she said, a bitter taste in her mouth. "That has not happened to me. What are you talking about?"

Edelgard turned to her, a deathly serious expression tightening her face. "Professor, I have a secret I would like to share with you. I implore you not to tell anyone."

Byleth nodded. "Edelgard, like I said, you can tell me anything."

The princess sucked in a deep, shuddering breath, then let it go. "I have kept it hidden all this time. But—" she held her hand up, and the Crest of Flames hovered in purple light above her palm "—I have a second crest. It's the same as yours."

Byleth's mouth fell open. While she had been ignorant in the past, she knew enough now to know only one crest could exist within a person.

"Do you remember how I told you my siblings all died from disease, injuries, or by going mad?" At Byleth's nod, Edelgard's jaw clenched. "I was twelve when my siblings and I were imprisoned underground beneath the palace. I have always possessed the Crest of Seiros, inherited through the Hresvelg bloodline. But it was only a Minor Crest. To endow us with the power of a Major Crest, the Crest of Flames, our bodies were cut open and violated, our blood spilt by the bucket for abhorrent experimental blood transfusions. For years, we were tortured and brutalised. I watched my siblings' bodies crumble, their hair turn white. My hair, turn white." Edelgard was gripping the ends of her ponytail. "It used to be brown… but now it's leached, colourless."

Byleth couldn't speak, the horror of Edelgard's words paralysing her.

"And here I stand, the fruit of that endeavour: Edelgard von Hresvelg. The future double-crested emperor, created out of pure greed to rule all of Fódlan. The success of an experiment birthed from the deaths of my siblings and countless other innocent lives." Edelgard met her eyes, a mockery of a smile on her face barely concealing her rage. "There you have it, the truth of the Hresvelg Empire."

A sudden anger boiled in Byleth's veins; constricted her chest. Anger she had only felt once, with terrifying consequences. "Who's to blame, Edelgard?" she asked.

The barely managed anger in her voice made Edelgard glance up in surprise. "Professor?"

Byleth took a deep breath and expelled it. "Who's to blame, Edelgard?" she asked again, much calmer.

"The prime minister and his gaggle of nobles," Edelgard replied, a flicker of confusion cracking her own mask of rage. "They had the Empire under their thumbs. My father was powerless to save us, his authority greatly reduced after an insurrection led by the Prime Minister."

"Ferdinand's father? Does he know?"

"He knows about insurrection. But not about the torture he sanctioned." Edelgard sighed. "Only Hubert knows."

"They have to be punished," Byleth said firmly.

Edelgard's lips curved into a wry smile. "Thank you for your concern, Professor. Rest assured, I will not forget what has been done." Then, her eyes grew flat. "When I manifested the Crest of Flames, I swore a silent oath for the sake of my family and all the poor souls whose lives were traded for my existence. For their sake, I will build a world where such meaningless sacrifice, all for the sake of having a crest, is never again sanctioned. As emperor, I will change the world. I swear it."

Edelgard meant every word. Byleth saw it in the way her face hardened, the stiff set to her shoulders, and the determination that radiated in every word. Here was a woman with two crests and a wealth of power, destined for a crown and a future she could mould to her every desire. But she had seen death and loss and suffering and refused to let them be in vain. Byleth now understood why she was so solemn, so determined, so ambitious; why she empathised with Lord Lonato even when she didn't agree with him.

"Professor?" Edelgard probed worriedly at her silence. "I didn't upset you, did I?" She dipped her head. "I must seem a horrifying aberration—"

"Don't say that," Byleth cut in. "What you said horrified me, not you."

"Oh," Edelgard bit her lip. "Thank you for your understanding. But I will assume from your reaction that was not the source for your Crest of Flames…?"

"Most assuredly not." Byleth looked at Edelgard and she looked back, their gazes locking for a long time. She was suddenly aware of the heat that their bodies shared where their arms pressed against each other. "I admire your resilience, Edelgard," she said, eventually. "And the passion you show to better the world… it's novel and wonderful to me."

"Oh," Edelgard said again, then blushed and looked away. "That's… thank you."

"Thank you for trusting me with this. If I'm able to, I'd like to help you in whatever way possible."

Edelgard stared at her for a second. Then the most radiant smile split her face, a smile that loosened all tightness in Byleth's chest, made her think she would do many things to see Edelgard smile like that again. "Thank you, my teacher," Edelgard said. "I look forward to your continued guidance."

Byleth nodded, and they fell into a quiet, comfortable silence.

"But Edelgard…" she said after a while.

"Hmm?"

"And here I thought you were the listening ear. Must you also outdo me in contemplative life circumstances like so?"

Edelgard flushed heavily. "I was not!"

Byleth laughed. "I'm just teas—what is it?"

Edelgard was staring at her, open mouthed. "I… I think that's the first time I've seen you laugh."

She blinked in surprise. "I laugh. Don't I?"

"I've not seen you do so before… you're often so serious." Edelgard's cheeks were still pink. "But in any case, it is nice to see you laugh. Especially after such eventful days."

Byleth chuckled. "Well, since you like it, perhaps I shall laugh more. Look less ghastly to you, I suppose."

"I don't think you look ghastly!" Edelgard gasped. "In fact, I think you look rather comely," she said in a softer voice, blushing again.

"Oh." Byleth's pulse stuttered unexpectedly. "Thanks."

Edelgard stood abruptly. "I should go! It's past curfew."

Byleth stared up at her, pulse still uneven. "Oh, alright. Ah, but Edelgard," she said quickly before Edelgard could leave. "Thank you, for listening and talking about things with me. I do feel better."

That made Edelgard relax, give a small smile. "You're most welcome. Goodnight, my teacher." Somewhat tentatively, she patted Byleth's shoulder, then left.

The comforting warmth of her palm lingered for a long time after.