Originally posted on AO3 not long ago. Now posting it here too. I fell in love with Three Houses (though I'm still not 100% done playing every route) and was inspired to do a Twin Byleth AU. So this story has the dual protagonists M!Byleth and FM!Byleth (Bylara). As one might assume, due to that major change as well as others, this isn't a direct novelization of canon game events. Canon is included to a point, then there's divergence. Pre-timeskip, the Byleths are 17. I know their age in game is supposed to be a bit of a mystery due to the circumstances surrounding their birth but here, Jeralt was telling the truth when he said he didn't have a child (or children here) until some years after leaving the Church.

Rating is subject to change depending on how the fic progresses.

Main themes are adventure/drama/angst/romance. In regards to the last one, all I ever really write is slow burn so expect that here. Plot and character development will take precedence at first. However, later on it does get a bit self-indulgent in that there may be quite a few love interests, namely with the characters I really like but haven't seen enough content for yet. I'm thinking at least one Byleth will get a small harem and I'm partial to it being FM!Byleth because I feel like right now there's more romance being written for M!Byleth.

Summary: Twin Mercenaries Byleth and Bylara are content with their life as hired blades, traveling with their father and his sellswords. But helping three young nobles launches them down a new path, one that leads to Garreg Mach Monastery. As they navigate political schemes and colorful students, persistent dreams and an intertwined destiny leave the future of the country in their hands for the shaping. Luckily the Goddess saw fit to give them each other to rely on, and a nifty ability that puts time on their side.

The ground was muddy and trodden, not even the smallest blade of grass poking through as thousands of booted feet marched across the great expanse to meet their adversaries. Steel sang through the valley as men fell from horses and others faced their end from the tip of a spear.

The whinnies of pegasi maneuvering around arrow projectiles as their riders fought joined the cacophony of noise. The size and intensity of the battle was at once horrifying and awe-inspiring, a once in a lifetime sight.

Through it all, a weapon glowing hotter than coal pierced the dark, smoke-charred sky, preceding the arrival of its fearsome owner. A grizzled man in pieces of armor, dirt marring his leathery skin, landed with a thud.

Dazed, enemy troops gave him a wide berth before regaining their mettle and charging forward to close the gap. The warrior rose, lashing out with his strange blade. Red light shone like the magic of a mage's spell, and where the segments of the blade traveled, soldiers fell. Through the path of the opponents he had felled, a woman stood, so poised and beautiful she looked terribly out of place amid the chaos and death on the field.

He charged at her, not batting an eye as a soldier fell at her feet, her name falling from his tongue as he perished.

She drew her blade and held it ready, pale green eyes flinty, her full lips pulled in a small scowl. With heavy feet he ran for her, cutting down the men brave enough to try to intercept him. Dawn broke as their eyes met, warm sunlight falling over them, somehow only making both appear more ominous.

Their single combat was a series of furious blows, neither gaining the true upper hand as they met in a shower of sparks with each heavy swing of their weapons. The fact that they were evenly matched drove their rages, until the man began to drive the lady warrior back, causing her to lose ground rapidly. Snarling, he flicked his blade, the orange sword splitting apart as it flew towards his winded adversary. She slid to the side in the last moment and instead of piercing her stomach, the sword snapped her belt. Another flick and he had wrapped the coils of his weapon around the shaft of her own.

She tossed her blade aside, and his, still coiled around it, came with it. Off guard, he had no recourse as she ran for him, delivering a punishing blow to his jaw and then leaping to smash both feet into his chest, bringing him to the ground. Scrambling to sit up proved a bad move when she brought a foot slamming down on his chest. Her blade followed soon after, and she leaned down into his face, beautiful and deadly.

"Tell me Nemesis, do you recall the Red Canyon?" she breathed through clenched teeth. His gold eye widened, recognition briefly flickering through it. "You die for that!" Her blade drove through him with a squelch. "Die!" He groaned, beginning to choke blood. "Die!"

Another stab. Sunrise broke on the battlefield, illuminating the body of the nearly-dead man underneath her, and her face pinched in pain. "You took…everything I loved!" The final strike held the most vehemence, cutting the death rattle short.

Panting hard, she came back to herself to see both armies were only watching them. Finally, cheers and raised banners signaled the end of the battle, and her mint leaf hair fell over her shoulders as she turned solemn eyes to the blade her opponent had left behind. Delicately cradling it to her face, heedless of the crimson still staining it, she sighed. "He's gone now, Mother." she promised.

Light and sprinkles of color warped the image of the quieting battlefield, flashing fragments in fractured hues sucked at the edges of the scene.

"Hey. Time to wake up." A gruff but caring voice, one so familiar it was recognizable to them anywhere. No longer on that battlefield, but in camp, where their father and other mercenaries were cleaning up and preparing breakfast.

Groggy, Bylara cracked her eyes open, her vision blurry with sleep but still able to mostly make out the form of the person on the bedroll beside hers. His midnight blue mop of hair, the exact color of her own, fell into his peaceful face. "Brother," she smacked at his arm. "Morning."

Between the two of them, she had always been the lighter sleeper, and so it was no surprise when her twin merely turned his back to her and slumbered on.

Her eyes narrowed. 'Is that the game?' She was very familiar with her brother's sleeping habits, rolling to pounce onto him, and unsurprised when his reflexes kicked in and he pinned her with a grunt.

"This game grows old…" he muttered, eyes half-lidded.

Their arms grappled, keeping him from pressing his full weight onto her.

"So does your oversleeping!" she returned, tossing him away from her and watching his larger body roll across the ground until he stopped on the grass, eyes to the sky…and right at their father's feet.

Jeralt sighed, hands on his hips. His dark eyes swept over them. They didn't look a thing like their father, who still had his butternut hair and beard without a streak of gray. Bylara and Byleth had come to the conclusion that they must both get their coloring from their mother.

Their mercenary skills, though, were entirely from Jeralt. He'd taught them all they knew, and even now they still learned watching how efficiently he could cut a line through a wave of enemies. There was no sign of him slowing down soon. In fact, aside from the lines carved around his mouth and eyes and the few, thin scars, there were very few indicators of his age, and it was a mystery they had long since stopped pondering on.

"What exactly am I supposed to do with the two of you?"

Byleth sat up, running a hand through his hair to dislodge any blades of grass.

Bylara sat cross-legged, turning her nose up. "Teach your son that a mercenary who sleeps deeply is asking to be gutted."

Byleth's eyes lazily drifted her way. "I would wager you only woke up slightly before me…"

"Alright, alright," Jeralt groaned. "Sorry I asked. You never do get tired of antagonizing each other, do you?" Even as he spoke, a barely-there smile was on his lips.

Byleth rose and stretched, arms straight above his head as his back popped. Bylara stood with her legs shoulder-width apart and leaned to the side in a stretch. First the left arm above the head, then the right.

"Any unusual dreams to report?"

"I dreamt about a battle unlike anything imaginable…Thousands and thousands of soldiers fighting in a big empty valley." Bylara found herself saying absently. "And the sword…"

"I dreamt of a girl with green hair on a throne." Byleth stated.

As always, their father met their words with a concerned furrow of the brow. "If it's the same battle you've been dreaming of all this time, then I have to say I'm at a loss. I haven't heard of a battle of that magnitude happening since the war nearly three hundred years ago." He turned to Byleth. "And your mystery girl…you've described her to me before. I still don't think I've ever met anyone like that."

Byleth's face didn't move, but she could tell he was still in deep thought. Their father could too; he was too adapt at seeing right through the both of them. "In any case, just put that out of your minds for now. The battlefield is no place for idle thoughts," They nodded slowly in agreement. Jeralt began to walk camp and they followed, "Risking your life is part of the job for mercenaries like us. Letting your mind wander is a sure way to get yourself killed."

Bylara didn't need to look to know her brother was staring straight at her now. How rude. So she was prone to daydreaming from time to time. It had still been her that once saved him from an out of control Pegasus while he was off in his own world.

"Ok, time to get moving. Our next job is in the Kingdom." Stopping short, Bylara stared at her father's back in silent surprise. The Kingdom? That far? Just as quiet, Byleth was considering their destination too.

"I told you before, it's far from here. So we'll need to leave at dawn." Jeralt continued.

"Of course." Byleth said, smoothly.

"Uh, sure…" Bylara nodded.

"Hm?" Jeralt glanced over his shoulder. "Good grief. Everyone is already waiting around for us."

The twins bowed shallowly. "Sorry…" they muttered.

"Just…" He rubbed at the back of his head, right above his short braid. "Byleth you can make sure the horses are all ready for the trip. Bylara, why don't you go down to the river and fill up all the canteens. It'll probably be a hot one today. I'll go make sure there's something left for you to have breakfast on the road."

All in agreement, they set to work on their respective tasks. Bylara passed their bedrolls and packed them up, then took the canteens for the short trek to the river nearby.

Meandering through camp, she got plenty of smiles and greetings from various members of their party. These men had seen her and her brother grow up, watched them become the fearsome Ashen Demon Duo they were today.

Bylara hummed to herself, a tune she wasn't quite sure where she picked up, coming to the last copse of trees that separated the camp from the riverside. The birds were starting up their daily songs, and the crisp grass underneath her feet smelled ripe in the April sun.

Careful to avoid rocks, she crouched by the calm river and uncapped the first container. It didn't take long to fill, and she replaced the top and set it on the bank beside her, reaching for another. Bylara had just finished unscrewing that canteen with steady hands, when the trees rustled and hurried footsteps reached her ears.

She'd think nothing of it normally. After all, they had made camp with plenty of other people. But the short pants that accompanied the quick pace was worrisome. Abandoning the canteen, she got to her feet, giving the forest an eagle-eyed glance.

There! She gasped. Someone was definitely running closer. One minute she thought she saw a flash to her right, then her left. Whirling around in a circle, she reached for the blade at her hip, thankful that her father had drilled caution into them. Even with a quick trip to the river, the tides could swiftly turn.

"Show yourself." She demanded, not expecting for the declaration to be followed by her on the ground and wheezing moments later.

Some yellow flash had collided with her, the sturdy weight of a warm body pushing her flat on her back. "Well hey there," a boy grinned down at her, the small braid at the side of his face tickling her throat as he sat up. "Don't mind if I drop in, do you?"

Bylara studied his playful green eyes, tanned skin, and the messy style of his short, dark hair. She'd never seen this character around the campsite or the village just beyond it before. Managing to wiggle her arm free, she took up the sword she'd dropped and tapped him lightly, careful of the tip. "Get off."

He obliged, even helping her onto her feet without waiting for permission. "Yeah, sorry about that. Not my best entrance. But kind of in a hurry," He glanced behind him and frowned. Curiosity overcoming her aggravation, Bylara followed his eyes. "I've been separated from my traveling party, and now it looks like my friends too. We got chased by some bandits that saw our clothes and decided we'd make good targets."

Bylara took the chance to appraise him, noticing for the first time that while he was indeed wearing a short yellow piece of fabric that tucked into his shirt and rested over his shoulder, his sleek black uniform was far too striking to belong to anyone other than a person of high standing. Too young to be an official, but maybe a noble? But his blasé attitude…

"Think you and your party might be able to lend a hand?" Again his demeanor was so casual. So unlike what she'd expect from a noble. "Well, you know, assuming you've got one."

"I have one." she said. "They're just up ahead. And if you and your friends are so valuable to them that they're chasing you down, then the village near here could be in trouble."

"I wouldn't doubt it," he shrugged. "The bandit's leader seemed like an unhinged, relentless guy. Not the type that would lose sleep over hurting whoever got in his way."

Bylara shook her head, already starting to jog away from the bank. "Let's go regroup with my party. Maybe your friends have already found my father and the others."

When she glanced to her side, she noticed that not only was he easily following, but now holding a simple bow at the ready, the quiver of arrows on his back noticeable for the first time.

At least she wasn't dealing with someone who was totally defenseless.