So I've seen many crossover fics where the FFXV boys are in the world of Remnant and not as much where the RWBY girls are in Eos. Then I started thinking that if I wanted to read that story, I should write it myself. So here we are!

I have to say, I'm both excited and nervous to write this story. I'm either going to write until it's finished or just give up half way (hopefully the former).

Also, this is a superlong prologue (four-thousand-and-something-words, not including notes, just a pre-warning) but I wanted to get it all in one chapter.

Disclaimer: I do not own RWBY or Final Fantasy XV and their respective characters and stories. They belong to © Rooster Teeth and © Square Enix respectively. This is not endorsed by Rooster Teeth in any way. Views, opinions, and thoughts are all my own. Rooster Teeth and RWBY are trade names or registered trademarks of Rooster Teeth Productions, LLC. © Rooster Teeth Productions, LLC.

M.E. 741, Lucis, 9:43pm

The cold, chilling rain was pouring down upon the kingdom of Lucis late at night. People were either rushing for refuge from the rain or were on their way home from their work. However, Cor Leonis was neither the former or the latter. Instead, the marshal of the Crownsguard was on patrol at the edge of the city, near the Wall that protected Lucis from any threats. He was very focused on his task, not letting any distractions hinder him as he was looking out for any possible threats. He found nothing of the sort, of course, since the Wall provided both protection and peace for the citizens.

When he finished his shift and headed backward to the Citadel, something strange caught his eye. Whilst the majority of soldiers were still on guard, a few of them were huddled around something, confusion drawn across their faces. Cor pushed his way through the small crowd so that he could get a better look. "What's going on here?", he demanded.

Just as he was about to get a response, the sound of high-pitch crying answered for him. He looked down to find a small box and when he knelt down another loud cry joined the first one. What he found bewildered him: two babies bundled up in blankets were cuddled up next to each, crying their little hearts out. The first one was a girl with bright blonde hair and lilac eyes and the one next to her was a slightly smaller girl with dark red hair and peculiar silver eyes. Cor leaned over the box slightly, trying to shield the children from the rain as best as he could.

"What is the meaning of this?", he asked in disbelief.

"We just found them here, sir.", one soldier answered.

"Did you see anything or anyone suspicious?", the marshal asked.

"No, sir."

Cor narrowed his eyes at the children. He had wondered how someone could've dropped off the children right by the Citadel without anyone noticing. And the fact that the children, blankets and box were barely drenched leading Cor to believe that they must've been dropped off recently. But by who?

A quiet sniffle snapped Cor from his thoughts and saw that the babies' crying had cease. The one with the silver eyes looked frightened and miserable and Cor couldn't blame her; being abandoned in the dark, cold night must've been terrifying for the small child. Looking to the blonde one, he saw that she was looking up at Cor with interest although her eyes were tired and puffy from all of the crying.

His attention then went to the blankets the two were bundled up in, seeing a small piece of paper attached to each one. The words were slightly smudged from the rain, but Cor could just about make them out.

The redhead's one said: Ruby.

The blonde's: Yang.

After a few more moments, Cor got to his feet, bringing the box up with him. He decided to take them inside with him and see if he could find any records of their parents or families. If he couldn't, the least he could do was look after them until he figured out a plan. "Return to your posts. I shall deal with the matter." The soldiers nodded reluctantly and left Cor with the children.

"C'mon.", he said. To his surprise the two babies had huddled together making a tangled mess of their blankets and had fallen back to sleep, uncaring of the coldness around them. "Let's see if we can find your parents." He couldn't imagine what they could possibly be feeling.

Readjusting his jacket over the sleeping babies so that rain wasn't hitting them, he made his way into the Citadel to find any information on the children.

He didn't find anything at the Citadel.

Cor had spent the last few hours going over the records of children born in the last few years but hadn't found anything on 'Ruby' or 'Yang'. He had tried everything from different versions to different spellings of the names in case he read the notes wrong. But no, these children were not from Lucis. The soldier was now wondering where these kids had come from, but the only explanation he could come up with is that they weren't born in the kingdom. However, this then got him to wonder how they could've gotten past the barrier. He buried his face into his hands. This was getting complicated.

A slight gurgle drew him from his thoughts and looked at the box of two children next to him. Ruby had woken up and instead of crying out like Cor expected her to, she started giggling and held her arms out as if wanting him to pick her up. Sighing, he gathered her up in his arms and began rocking her back and forth, unsure of what to do. Yang had also woken up and was looking at the other baby with narrow eyes, as if jealous.

Cor remained this way for a while before looking at the child and noticed something… off.

Readjusting the blanket, he could see a mysterious necklace around the baby's neck. In any other circumstance, Cor probably would've thought nothing of it but something about this necklace threw him his off a little. The small crystal resting on her chest was glowing a bright red, giving off a pulsating hum and Cor could feel a warm energy radiating off of it. He hovered a finger over it and found that it gave him a small zap in reaction. Looking at Yang, he moved her blanket around and saw a similar one around her neck, only this one was a golden yellow.

He put Ruby back down next to Yang, who fumble embraced the smaller baby, letting a small laugh. If these necklaces were potentially magic this just opened a whole new array of questions as to who these children really were.

A small knock broke the silence and a guard quietly stepped in. "Yes?", Cor asked.

"Cor Leonis-", the guard said. "-the king requests an audience with you." His gaze went down and Cor followed it, realising that he was looking at the laughing babies. Cor groaned internally. He had turned up to the Citadel with two random babies, of course that was going to raise some questions.

Clearing his throat, he straightened up and picked up the children. "Of course. I'll be right there."

Cor stood uncomfortably in the middle of the throne room with King Regis Lucis Caelum sitting at his throne, looking at the younger man with bewilderment and disbelief. The awkward silence was broken by the children laughing, causing a few guards at the door to chuckle in response and ceased their laughter before Cor could turn around and give them a chilling death glare.

"Care to explain, Cor?", the king simply asked.

The man shifted his weight onto one foot. "They were found outside the Citadel." Regis made a gesture with his hand, as if prompting him to continue. "Their names are Ruby and Yang. There are no records on them or their families."

The king nodded in understanding and motioned for Cor to bring them closer. He stepped up to the dais and Regis looked into the box. The two babies cooed at the sight at Regis and the king gave them a friendly smile.

"The only explanation I can think of is that they were born outside the city."

Regis furrowed his eyebrows. "If that's the case then how could they have passed through the Wall?"

Cor shook his head. "I do not know, Your Majesty." He looked down at the children, remembering the other thing that he found. "But there is something that you might want to see." He reached into the box and moved the blankets around so that the king could clearly see the glowing crystal each baby had.

The marshal could already see the change in the king's face as he took in the sight. Regis reached out a hand towards the two. The ring on his finger pulsated with magic as it got closer and the red and yellow light glowed even brighter, the warm glows overlapping each other. The king recoiled.

He could sense a magic not familiar to him but it didn't feel dark. If anything it felt like light energy, like the one he was used to using. Nothing about the children struck him as dangerous or destructive about the children or even the crystals. However, they were obviously not of their world.

The children looked up at the king again and giggled. Ruby reached out a small hand reached out and grabbed hold of one of the king's fingers and suckled on it whilst Yang reached up to pat his hand, giggling loudly. Both children were oblivious to the troubles around them and Regis smiled softly at them.

If two mysterious children showed up on his doorstep with a magic like he had never seen before, Regis knew exactly what to do next. He looked at Cor and slowly reached his arms out towards the box. "May I?", he asked.

Cor was caught off guard for a moment before nodding. "Of course, Your Majesty.", he replied and then wordlessly handed the children to the king.

The king stood up and began to descend the stairs. "If you will excuse me, Cor." He didn't wait for the marshal to answer.

It was peculiar for King Regis for approaching the Crystal chamber late into the night but none of the guards questioned him. He made his way down the walkway with the two children in his arms. As he walked, Ruby and Yang seemed to be squabbling but at the same time… not. They were lightly hitting and knocking each other on the head but were squirming and giggling whilst doing it. Regis shook his head. His child, Noctis, was just as fussy at this age.

He stopped in his tracks when he was directly in front of the Crystal. It was glowing bright blue, purple and red colours and the light radiated from the large gap of the Crystal. Regis looked down, not wanting the Crystal in his sight.

"You know why I'm here, don't you?"

A few beats of silence and a deep, guttural voice came from the Crystal.

"Yes, I do."

"What reason do you have to send these two innocent children to my doorstep?"

"A looming darkness threatens this world and another."

"Another?", Regis interrupted.

"The prophesied King of Light is destined to restore the light to the world. The King and Oracle must stand together to save the two worlds but they cannot do it alone. Four girls have been sent from the other world to assist them and the power they hold shall assist in the fight against a long forgotten darkness."

"King of Light… long forgotten darkness…", Regis repeated, trying to make sense of what he was hearing. He didn't fully understand what the Crystal was saying and was dreading what would come next.

"Come forth, king, and see for yourself."

The voice went silent.

Regis looked down at Ruby and Yang, who now looked as if they were cowering in fear of the low, booming voice and he could understand why. He quietly soothed them before walking closer to the Crystal, one arm extended out.

His hand was only inches away from touching the glowing rock and a warm light enveloped him.

Cor didn't see the king leave the chamber for three hours since he entered. He was pacing back and forth outside, unsure what to make of the whole situation. He and Regis had silently agreed that something was off about the children's sudden appearance and the magic they seemed to be in possession of.

But they also agreed that there was nothing dangerous about the children. They were only babies, they would pose no threat to them. He wondered where they came from and who left them there. Were they intentionally left there for them to find? Given the strange crystals they were found with, that felt familiar to the magic they used, it was was definitely a possibility. Hopefully, Regis' 'encounter' with the Crystal would shed some light on what was going on.

The click of the door caused Cor's head to snap up to find Regis reemerging from the chamber, cradling the box still holding the children in one arm and closing the door behind him with the other. The corridor was dimly lit, but the marshal could see the king's eyes puffy and red, as if he had been crying. What did he see to cause such a reaction?

"Your Majesty?", he asked reluctantly.

The king smiled at him and Cor didn't mention the fact that he could clearly see the sorrow behind his grin.

"What I saw…" He looked down the floor trying to regain his composure and looked back up after a while. "It is best if Ruby and Yang stay here. Where they shall be safe." Regis could see that Cor wanted him to elaborate, but the king shook his head. "I apologise, this is not the time to talk about it, Cor."

On instinct, Cor quickly bowed. "N-no, I-I understand, Your Majesty." When he straightened up, his eyes softened. "If there is anything that I can do…"

That night, Regis quietly thanked Cor for his assistance and relieved him of duty for the night, promising that they would discuss the matter in the morning.

Regis briskly walked down the corridors of the palace until he abruptly stopped at the door of his son's room. He stood there for what felt like hours before he mustered up the courage to quietly open the door and enter Noctis' room. He gingerly eased himself down the edge of his bed and carefully ran a hand through his raven hair.

The contact caused the young boy to stir and his eyes fluttered open, revealing vibrant but exhausted blue orbs. He groaned and when he felt a weight on the end of his bed, he slowly sat up, rubbing his tired eyes. He was a little caught off guard to see his father there with a small box beside him. When he was about to ask his father what was going on, he caught himself when he saw that he looked like he had been crying.

"Dad?", the young prince asked. "What's wrong?" The second the words left his mouth, Regis wrapped his arms around his son. He held him tightly as if letting go would cause him great harm. He sat and simply held him and had to hold back the fresh tears threatening to spill out. Noctis spoke again, but Regis didn't catch what he said and wordlessly released his son, one hand on his shoulder and the other cupping his face.

The prince's eyes travelled to the box his father had carried in and after readjusting his sight from sleep, he could see two babies. His eyebrows furrowed in confusion. "Dad, who are they?"

Regis smiled gently and set the box in between them. The babies were now sitting up and their eyes instantly brightened at the sight of Noctis. They babbled excitedly and the young boy reluctantly reached out to them. The redhead had latched onto his hand, like she did with Regis, but the blonde one reached out and gently patted Noctis on the cheek. The boy let out a surprised laugh, causing the babies to laugh as well. Noctis slyly repeated the child's action and then squeaked when the other suckled on his pinky.

The king smiled, joyed to see the three children getting along so well already.

"Son, this is Ruby.", he gestured to the redhead. "And Yang.", and then to the blonde.

Perhaps they could help his son in ways that he couldn't.

"Your new sisters."

M.E. 741, Tenebrae, 10:23pm

In Fenestala Manor, Lunafreya Nox Fleuret was fast asleep in her bed chamber. The moonlight was peeking in through the windows, bathing the room in a soft blue glow. Her long blonde hair was splayed over her pillow and the young girl was curled up under the blankets.

The peaceful silence was disturbed when a cream coloured dog slipped into the room and quietly padded over to Lunafreya's bed. The dog put her front paws on the edge of the bed and whined, quietly nudging the girl with her nose.

Lunafreya stirred and woke up confused to see her dog this late into the night. "Pryna?", she asked tiredly. "What is it?" The small dog didn't answer. Instead she nudged the princess' hand as if trying to coax her out of bed. Lunafreya was too exhausted to comprehend what her dog wanted and was on the verge of falling back asleep again. All of a sudden, Pryna jumped up onto the girl's lap, causing her to squeal in bewilderment. The dog began barking at her and Lunafreya tried to quiet her down before she drew attention to them. Pryna jumped off of the bed and shuffled to the door, still barking.

The princess groaned internally. It seemed that Pryna wouldn't leave her alone until she saw what she wanted. She just hoped that it was important.

She slipped out of bed and put on her slippers and nightgown before stealthily easing herself out of her room and followed the dog down the hallway. Pryna practically bounded down the corridor whilst Lunafreya tried to jog as quietly as she could.

Her jaw practically dropped when she realised that her dog had led her to the garden. She reluctantly turned her head back, watching out for anyone that might catch her. She stepped out into the garden, the blue sylleblossom flowers tickling her legs.

"Pryna.", she called out, her voice barely above a whisper. "What are you trying to show me?"

The dog lowly whined in response and was surprised to hear another growl in response. Picking up the pace, she saw something that surprised her beyond comprehension. A small black and white dog was curled up against another young girl who couldn't have been more than four years old. The smaller dog perked up at the two new faces and growled, standing protectively in front of the small girl.

Lunafreya slowly inched forward with a hand out to the dog. "It's okay.", she soothed. "I'm not going to hurt you." After a while, the dog sniffed her hand and hesitantly nuzzled it. Having the dog's trust, Lunafreya made her way towards the small child.

The girl was sniffling softly and her face was buried in her hands, soft white hair covering her face. "Hello?", the princess asked. The child's head snapped up, revealing inquisitive blue eyes. Her face scrunched up like she was about to cry.

"It's alright. I won't hurt you.", she said with a friendly smile. She reached out a hand and, after a moment of reluctance, the girl with white hair took her hand. The two children sat there quietly for a moment, their dogs watching them intently. A few beats past and the smaller girl began to cry and wrapped her thin arms around the princess' waist.

Lunafreya was caught by surprise but soon regained her composure and rubbed the girl's back in comfort. "Shhh.", she hushed softly, trying to calm her down.

The two of them remained that way for a short while until she heard some rustling from behind her. "Sister? What is the meaning of this?" Lunafreya turned around to find her older brother, Ravus, standing behind her with a stern expression. "The servants told me that you left your bed chamber to follow Pryna out of the manor."

The child squirmed and clung to the princess tighter. "I found this girl lying in the grass. I do not know where she came from."

The older Fleuret sibling's expression softened when he saw the frightened child. He knelt down next to his sister. He looked between her and the young girl. "Who do you suppose left her here? How could they have gotten into the manor."

Lunafreya shook her head. "I do not know, but if she was left here then maybe we were meant to find her." She looked to Pryna, who was sniffing excitedly at the other dog. "What do you propose we do, Ravus?"

Ravus sighed. "I suggest that we tell mother of this matter immediately. It does seem a tad suspicious that a random child was left in our garden of all places."

"Weiss.", a third voice interjected. The two siblings whipped around to see a tall woman with long jet black hair wearing a black and gold dress with a white shawl draped around her back and over her arms. She knelt next to the children as she spoke softly. "Her name is Weiss and her dog is named Zwei."

"Gentiana?", Lunafreya asked in disbelief. "How…?"

The older woman smiled and pointed between the two of them. "There's a note on grass and a tag on her dog."

"We need to help her, Gentiana.", Lunafreya immediately exclaimed. "What should we do?"

The woman's expression softened and motioned for the princess to hand the child over to her and 'Weiss' reluctantly wrapped her arms around her as Gentiana picked her up. "Leave it to me.", she said and the the siblings followed her back into the manor.

"So you found her in garden?", Queen Sylva asked. Gentiana was still holding Weiss, who was on the verge of falling asleep. Ravus and Lunafreya were standing both sides of her.

"Yes, Pryna led me to her, mother.", Lunafreya answered. "Her name is Weiss."

The queen of Tenebrae frowned slightly as she approached them. Weiss looked at Sylva with curiosity and nervously bit her nails, unsure of what was going on.

"We cannot simply leave her, mother.", Ravus added. "If she's an orphan, she will not have any place to go."

"And look how Umbra and Pryna are getting along with Zwei!", Lunafreya exclaimed, pointing to the group of dogs that were playing together. "It's like they're friends already!"

Sylva sighed and reached out to stroke Weiss' soft hair, causing the girl to relax in response. Her smile was infectious as it caused Lunafreya, Ravus and even Gentiana to smile as well. The queen's eye caught a glowing light blue crystal around her next, piquing her interest. She could sense a strange energy radiating off of it, like nothing she had ever seen before. Her eyes met Gentiana's and was met with a expression that said that both women knew more than they were letting on. It was definitely not a coincidence that Weiss was found with a potentially magic crystal near their manor, home to the line of the Oracle.

She regained her composure and gave Weiss a loving smile. "Well, if we cannot find her parents, Weiss is more than welcome to stay here."

Lunafreya beamed and looked up to the younger girl. "Weiss?", she asked.

The white-haired girl looked to each person one by one before looking at Lunafreya and returned her smile. "Yes please.", she said shyly. "I'd like that."

M.E. 741, Niflheim, 8:54pm

In the capital city of the Empire, Gralea, Verstael Besithia was hard at work in the laboratories. Part of the time, the Emperor or other high-ranking authorities would give him a new task to work on, but mostly they left him to his own devices. He was shuffling around in his red clothing and cape writing down notes and pressing various buttons on several devices.

"Besithia? Hard at work?", a low voice asked.

The researcher looked up from his work to see a familiar dark purple-haired man dressed in his usual flamboyant clothes and scowled. "Chancellor Ardyn Izunia? What reason have you got to be in the laboratories this time of night?", he snapped.

The chancellor pouted and put a hand over his heart. "Such harsh words, Besithia. I'm hurt." He dumped a large box onto the table. "Even after I brought you a gift."

Verstael frowned and pulled the box closer to him to examine. Opening it up, he wasn't sure of what he would find. He definitely expect to find a child. She looked to be about four years old. She was lying fast asleep in the box, covered in grime and dirt, clothes torn and ripped and black hair cascading over her slim shoulders. "A child?! Is this some sort of joke to you, Izunia?!"

"Besithia, please, not so loud. Blake will be offended if you call her a 'joke'.", Ardyn said mockingly.

"'Blake'?"

"Your new… pet project.", Ardyn replied slyly.

Verstael crossed his arms. "And why should I care for a common street rat?", he spat.

The Imperial chancellor raised an eyebrow before readjusting the excuse for a blanket the girl was covered with. Verstael's eyes must've been playing tricks on him; the girl had cat ears.

The scientist stuttered. "Is this child a daemon or something?"

Ardyn shook his head in amusement. "She is just as human as anyone else.", he said with a chuckle. "I thought she'd be of use to you." The scientist examined the girl: yes, she had the ears, but everything else about her appearance wise pointed to this 'Blake' child being a mere human.

"Anything else?", he asked.

The chancellor bit his lip as if in thought and then shrugged. "No. Nothing that comes to mind." Not even a beat later: "Oh!" He pulled out a small purple crystal attached to a silver chain and dangled it in front of the scientist. "This was found on her person."

The dark crystal thrummed with a low groan and when Verstael touched it slightly, it almost felt like he was burned. He recoiled. "Lucian magic?", he asked in disbelief.

Ardyn quickly pulled the necklace back. "No, something better."

Verstael reeled back. "Alright, what do you want, Izunia?"

The chancellor gaped exaggeratedly. "What makes you think I want something?" He could tell that Verstael wasn't buying his innocent act. Ardyn smirked. "Besithia, I have a proposition for you: I handle any matters to do with this…" He twirled the chain of the necklace around his finger. "… 'magic', and I will ensure that the Empire will allow your experiments on Blake, under my supervision, of course."

The scientist blanched. "Is that all?", Verstael asked incredulously. The chancellor nodded. "Then so be it."

Ardyn made a bowing action whilst taking off his hat and holding it to chest. "I promise that you will not regret this, Verstael.", he said as sincerely as possible. He replaced his hat on his head. "I'm sure Blake will help the world in great ways. I hope she proves to be more successful than your other experiment." Verstael's eyes flashed with anger but didn't say a word to the chancellor. And with that, Ardyn Izunia exited the room.

He heard the girl stir awake and had curled up into a ball in fear when she saw Verstael. The man knelt down so that he was at eye level with her and tried to to smile as friendly as possible. "Hello, Blake. My name is Verstael. You were brought here when you found on the streets all alone."

Blake scratched behind her ear as she looked around. "Where am I?"

"This is Gralea, the most secure place in Niflheim." The child tilted her head to the side in confusion. "Do not worry about that, Blake. I can assure you that you are perfectly safe here." Blake rubbed at her eyes tiredly. "I would like to just run a few tests and to make sure that you are healthy. Is that alright?"

Blake stared at him and then nodded hesitantly. He seemed nice enough, she could trust him, right?

"Thank you, Blake." Vestael soon began extracting a few blood samples and then attached an IV line to her arm that administered medicine and nutrients to the pale and sickly child. Once the test results came back, the scientist couldn't believe his eyes. Blake's blood definitely wasn't human but it wasn't daemon either. She was something else, a completely different species. He couldn't believe the opportunity that had been presented to him. An inhuman person had been delivered to him and he was going to be the one to unlock the potential and mysteries behind it.

"You are really special. Do you know why, Blake?" The child shook her head. "Because you, my dear, are going to help change the world."

Outside the laboratory, Chancellor Izunia held the crystal up to eye level and chuckled sinisterly.

That night, the fate of two worlds had been decided.

Side notes: I have changed the the girls' ages that will differ slightly to each other (during the game's main story), there is a reason why Weiss has Zwei instead of Ruby and Yang which will become apparent later and (completely irrelevant note) writing Verstael totally makes me think of the song 'Lusus Naturae' (from Grimm Eclipse).

What do you think? Should I continue? Would love to hear some feedback!