Howdy, all! Welcome to my first attempt at a Crossover story! I actually have a few crossover ideas to mix RWBY with other medias, but this is the one that won out! And that is largely thanks to ThatOnePsycho, whose story gave me solid ideas I felt a need to instantly pursue. This may even be one of my longer fics. There will kind of be two parts to it, with the second more than likely sectioned off as a sequel down the line. This first part will focus more on the RWBY side of things with Ruby trying to keep the right secrets while at Beacon. I hope you all enjoy!
Kairi smiled as she watched the gentle ocean from the beach shore. The excitement of visiting a brand new world never ceased to excite her, and this place in particular reminded her of her childhood playground on the Destiny Islands. Peaceful memories flooded the redhead, times of her and her friends. From before their world was turned upside down. From before the Keyblade. From before Xehanort's war. And some from after, too. After the guardians of light saw the other side of that war as it's victors, allowing Kairi to enjoy simple moments like this without guilt.
A digital jingle sounded in Kairi's pocket. It brought her back to reality and reminded her that even though they have achieved a greater peace, there was still work to be done. Work that a Keyblade wielder like her should be getting back to. She pulled out the noisy device, her Gummiphone, and answered the call. Aqua's face appeared on the screen.
"Hello, Kairi," Aqua greeted.
"Master Aqua!" Kairi called out, "It's good to hear from you."
"How are things going?" Aqua asked politely.
"I thought you weren't allowed to help me on my Mark of Mastery?" Kairi teased.
"Who said I'm helping?" Aqua smiled, "I'm simply… asking for a status report. Besides, after all you've been through, we've all been though… Your formal exam is rather simple for a reason."
Both girls shared a small giggle.
"So?" Aqua picked back up, "how are things?"
"This world is an interesting one," Kairi began, "I believe it's called 'Remnant'. It's a very large world with it's own magic and troubles."
"Like what?" Aqua was intrigued.
"Well, their magic is based on some kind of natural crystal they mine, I'm not entirely sure I understand it," Kairi explained, "as for their 'troubles', there are monsters native to this world that they call 'Grimm'."
"'Grimm'?" Aqua asked for elaboration.
"They're not too different from heartless," Kairi continued, "they're creatures of darkness, all black, without hearts and apparently soulless. But instead of seeking hearts for themselves, all they crave is destruction."
"That is interesting..." Aqua face was thoughtful. "I, personally, have encountered few worlds with natural threats on par with heartless or the unversed."
"Don't forget the nobodies!" A voice behind Aqua piped up, either Ventus or Roxas, though which of the two Kairi could only guess without seeing them.
"Because of these 'Grimm', the people of this world have developed a warrior class they call 'Huntsmen', who specialize in studying and fighting them." Kairi concluded her findings.
"Perhaps we misjudged," Aqua responded, "mistook these Grimm for heartless. Perhaps the threat to that world is not as grave as we assumed."
Kairi shook her head. "I've definitely encountered heartless in my time here. There are very few of them compared the size of this world, but they exist."
Another face appeared on screen, and Kairi could now tell the other voice was Ventus. "Maybe this 'warrior class' has something to do with that?" he posited.
Aqua took her friends theory into account. "Worlds with similar specialized soldier castes tend to have an inordinately high number of fighters. It is possible they've been destroying heartless for years, all while assuming they were another kind of Grimm."
"A society of hero warriors could also easily lead to prospects," Kairi added, "for the next generation of Keyblade wielders, our future students."
"Let's tackle one issue at a time, Kairi," Aqua refucused her friends. "The heartless are on Remnant, and your mission still stands."
"Right," Kairi nodded, "I've traced a large concentration of heartless to a small island locally known as Patch. I believe the Keyhole is somewhere on this island."
"Good work," Aqua praised. "Remember, a world's heart is still only one heart. All it takes is a single lucky Shadow breaking through the Keyhole's natural defenses for darkness to swallow a world. Find it, seal it, and return to the Land of Departure as a Master. May your heart be your guiding key."
Kairi smiled as the call ended and put away her Gummiphone. A rustling in the bushes nearby caught her attention, and she turned in time to see a young girl, couldn't be more than five years old, with dark red hair and silver eyes staring at her.
Ruby Rose loved going to the beach. And her family lived so close that it wasn't even difficult! They weren't always happy when she went on her own, but she was careful! And she knew what to do if she saw a monster! There were no monsters today, so the young girl easily made it all the way to the water.
As she arrived, she heard a voice nearby. She was still in 'be careful' mode, and tried to approach quietly. What she found was a girl, either a teenager or a young adult, with bright red hair. She wore a hooded, pink, sleeveless mini-dress with plaid frills, as well as short boots. Various bracelets and accessories hung off her, and a petite pauldron with a large button adorned her left shoulder.
Ruby stepped on a twig, and the girl's attention was drawn to her. Not knowing what else to do, Ruby froze.
The girl smiled, her blue eyes shining. "Hello," the girl greeted. She knelt down onto her knees until she was looking up at the little girl. "What are you doing here?"
Ruby's eye lingered on the pocket she watched the girl put something away into. "Was that your scroll? That's a weird scroll."
Scroll? Kairi thought to herself. This world must have it's own version of a Gummiphone, which they call scrolls… "It's a very unique device," Kairi explained, not entirely lying.
"Are you a huntress?" Ruby asked in excitement.
"You could say that," Kairi answered confidently. "You could also say I'm on a secret mission," she added, bringing her index finger in front of her lips.
"Ohhh…!" the little girl became even more excited. "Wassayur name!?"
Kairi giggled, "If I told you that, I wouldn't be being very secret, would I?"
"But, but..." Ruby thought for a moment. "If I know your name, then I know when someone's askin' if I seen you! Then I could just say no!"
"But how can you know my name if you've never seen me?" Kairi teased further. She watched the little girl squirm for a moment while trying to come up with another excuse. Finally, the Keyblade wielder simply held up her hand. "My name is Kairi."
The little smiled and took Kairi's hand to shake. "I'm Ruby! Ruby Rose!"
"It's nice to meet you, Ruby!" Kairi smiled.
"Have you had dinner!? You could come to my place! I'm sure dad wouldn't mind a huntress joining dinner!" Ruby casually offered.
Kairi's stomach grumbled as if on cue. True, this island was small, but that didn't mean the Keyhole would be any easier to find. It's not like they tended to be in plain sight. If this little girl's father really would house her for the night, she could get some proper rest and be ready to search in the morning. "All right, Ruby. Lead the way."
Ruby's family turned out to be just her father and an older sister, both of which were blonde. They lived in a modest cabin outside of the main settlements. With the prevalence of the Grimm threat, Patch must be very peaceful indeed if someone felt comfortable raising their children in the countryside. "I am very sorry to impose, Mr. Rose."
"Eh, it's fine," the father, Taiyang, smiled. "Actually, you're not the first huntsmen Rubes has invited to dinner. And I do know how the life can get. And please, it's Xiao Long, not Rose."
Kairi tilted her head. She didn't have personal experience with 'family names', but she was sure the child shared their parent's last name.
"Rose was Ruby's mother," Taiyang explained, "We never married, and she… died a few years ago. Ruby decided she wanted to be a Rose, to honor her mother."
"That's very sweet," Kairi offered her condolences, "she seems to have a big heart, with lots of light to share."
"That's not very hard to see," Taiyang smiled.
"Kairi!" Ruby came running into the living room where Kairi and Taiyang were talking. "Are you staying for dinner!? Is she staying for dinner, dad!?"
"Well?" Taiyang looked to Kairi.
"As long as I'm not imposing," the young Keyblade wielder answered.
"Of course not," Taiyang assured her.
"Can I see your weapon!?" Ruby suddenly asked with stars in her eyes.
"E-excuse me?" Kairi was caught of guard.
"She's a bit of a weapons nut," Taiyang rubbed the back of his head in embarassment. "She loves, loves, loves them. Can't wait to have her own one day."
"Isn't it impolite to wave a weapon in someone's home?" Kairi deflected. "But maybe, if you're good, I'll show you outside in the morning."
"Who says I'm not good?" Ruby asked, genuinely confused.
"Don't think I've forgotten you heading to the beach on your own again, little lady," Taiyang reminded his daughter, making the little girl freeze.
Kairi couldn't help but giggle at the interaction. She certainly could have found worse ways to spend the night than in company like this.
Morning came, and Kairi prepared to leave the house. Little Ruby and her sister were still sleeping, but she did encounter Taiyang on her way out. "I thought I was going to have to leave without saying goodbye," Kairi told him as she passed through the living room.
"Heading out already?" Taiyang asked. "Ruby would love to see you off."
"Unfortunately, I'm on a bit of a time crunch," Kairi admitted, "But after, I'll come say goodbye before I leave here, if I may?"
"Huntsmen are always welcome in my house," Taiyang informed her proudly, "and it would certainly make Ruby's day. She seemed to take a liking to you last night."
"In that case, I'll see you later." Kairi placed her hand over her chest and bowed her head slightly, "may your heart be your guiding key."
The phrase made Taiyang raise an eyebrow. He shrugged it off. Despite the unusual words, he could sense the benevolent intent behind them. "Good luck to you on your mission," he nodded in return.
With that, Kairi left. The Keyhole would not be easy to find, but perhaps someone in town could point her to old ruins or sacred lands. It wouldn't be the first time a Keyhole had become to center of a world's religion, if Master Eraqus's journals were to be believed. As she walked, she failed to notice a little shadow tailing her away from the Xiao Long house.
Kairi summoned her Keyblade to cut through the dense forest growth. After hours of asking vague questions, she finally got an answer she could work with. A part of the forest that, inexplicably, seemed more like a jungle than anything. Such a drastic anomaly in the ecosystem couldn't be explained, at least not by the science of Remnant.
Kairi knew different. She knew this kind of change could be affected by exposing the land to a world's heart. The kind of exposure that can be the result of the world's heart's own energy pouring through its open Keyhole.
Destiny's Embrace cut through one last vine, and exposed a cave entrance. Kairi could feel the raw light of the world's heart emanating from the cave in waves. "I've found it!" The young Keyblade wielder dashed into the cave excitedly. It was a small cave, only one larger chamber. At the far back was a glowing Keyhole with the world's energy slowly flowing outward. Kairi rasied Destiny's Embrace, but before she could summon her Keyblade's light, she heard a commotion behind her.
A familiar shape came running into the cave. "Kairi! Kairi, Grimm!"
"Ruby!?" Kairi was stunned. Had the little girl been following her all day, since she left the house that morning?
"Kairi! Grimm!" the little girl took cover behind the Keyblade wielder.
Kairi looked toward the cave entrance to see what had chased Ruby inside. A group of Shadows wiggled their way into the chamber. "Not Grimm," Kairi readied her combat stance, "heartless!"
The group of Shadows was no problem, each being dispatched with a single slash from Destiny's Embrace. But that didn't change the fact that the heartless had found the Keyhole. Kairi could not have been a moment too soon.
It also didn't change the fact a certain little girl had apparently followed her here. After quickly destroying the Shadows, she turned to face Ruby. "And just what are you doing here!?"
Ruby knew she was in trouble, but still wanted to explain herself. "Y-you left without saying goodbye… I just wanted to see your weapon..."
"Ruby..." Kairi sighed, "this isn't a game. You can't follow… huntsmen around on their missions. It's dangerous."
"I knew you'd protect me," Ruby argued.
"That may be," Kairi knelt down, "but now I can't focus entirely on my mission. Now I have to split my attention between doing my job and keeping you safe. And what if I fail? What if I got hurt and could no longer protect you? What if you got hurt? What would your family think? What are they thinking now, after you vanished on them?"
Ruby got really quiet. Kairi's words hit her like a ton of bricks. Of course she wasn't thinking about any of that.
Kairi heard something coming down the cave. Something bigger than a couple of Shadows. She quickly picked Ruby up and found a large rock she could hide the girl behind. "Now, you are going to stay here. I'm going to fight this monster, finish my mission, and take you home."
"But I want to help!" Ruby began to step out from behind the rock.
"Ruby!" Kairi used a harsher tone to convey how serious this situation had gotten. "The best way to help me is to stay hidden, so the monster doesn't attack you."
Ruby looked like she had just been slapped. She nodded slowly and slinked back behind the rock. Kairi felt bad about raising her voice at the girl, but there wasn't time to worry about that right now. She raised her kayblade and waited for the new heartless.
She didn't have to wait long. The sunlight from the entrance was blocked by a large figure. Some heartless take shapes related to the world they invade, and this one certainly looked like the Grimm Kairi had seen. If not for the heartless symbol adorning its wolf-skull mask, she may have even thought it was another 'Beowolf' herself. Other subtle differences was that this creature was a true quadruped, and a black and purple smoke escaped it's mouth with each exhale. It was also massive, but that was a less subtle difference.
It looked frightening, but by using Scan, Kairi could sense it's energy. It wasn't weak, but to the experienced Keyblade wielder, it wasn't impressive either. I've taken on stronger beasts than this, Kairi smiled.
The beast roared and tried to turn Kairi into paste with it's large, clawed paw. Kairi easily leapt between the claws as they came down. She fell towards the heartless's face, bringing down Destiny's Embrace as she did so. The strike disoriented the heartless, allowing Kairi to follow up with a six-hit combo.
The heartless jumped back after Kairi's combo and roared, covering Kairi in the smoke from it's mouth as it did so. Her skin began to sting, and she could feel her own energy being eaten away. She quickly jumped out of the smoke, though still felt her energy chip away for a few more seconds after she did so. So his breath hurts, and carries some poison properties. Need to stay away from that.
Meanwhile, Ruby dared to peek out of cover. She still wanted to see this fight, and honestly, how much more trouble could she even get in? And she was met with a treat as she saw Kairi throw a fireball out of her flowery sword. Where does she even keep the Dust in that thing?
"Fira!" Kairi shouted, the second-level fire spell leaving her Keyblade. It struck the heartless in the side of it's snout, forcing it to face away as Kairi ran at it. She collapsed into a slide with her Keyblade raised, slicing down the entire length of the monster's underside. After coming to her feet behind the heartless's back legs, Kairi jumped onto the beast's back. She ran back toward the front, cutting slices into the best with each step.
She once again leapt with the intention to come down on the heartless's snout, but the heartless wouldn't be caught by the same trick twice. At the last moment, it thrashed its head upward. Its snout caught Kairi around her middle and bounced her into the air. As she fell, it's claw swiped at her with enough force to send her rocketing into the wall almost faster than one could see.
Kairi fell to the ground and struggled to stand. She was not so much damaged as she was dizzied. But being dizzied still left one open, that much even Ruby could see. She could also see the beast slowly approach Kairi. Like with many things, Ruby then acted without sparing much thought to her decision.
"HEY YOU BIG MEANIE!" Ruby jumped out from behind cover. The heartless stopped and turned to face the new voice in time to see the little girl throw a rock at it. The rock fell pitifully short of striking the beast, and both Ruby and the heartless watched it bounce across the ground. The beast huffed and started to walk towards the child.
Kairi regained full use of her senses in time to see Ruby backing up against the wall. "RUBY!" Kairi cried, reaching out to the younger redhead.
Time seemed to slow. A feeling Kairi was only vaguely familiar with blossomed in her heart. A power flowed into her. The power to stand, the power to fight, and the power to do so much more. Kairi noticed she could still move easily while everything around her slowed to a crawl, and she swore she could see rose petals appear out of thin air.
To Ruby and the heartless, it was only an instant that Kairi appeared between the two, striking the heartless twice before it could even register the thought. She jumped backward with a Fira, further separated the monster from the little girl.
While the beast reeled, Kairi had a moment to think over what happened. She had activated a Link, but with who? Who did she even attempt to form a bond with? Sora? Aqua? But this wasn't either of their power…
The monster stared back at her, and Kairi settled with figuring this out later. For now, she could feel the benefits of the Link. Whoever she connected to had decent strength, but a truly impressive amount of magic reserve. So she decided to use that magic.
"Blizzaga!" Kairi froze the left side of the heartless's face solid. She rushed, striking the ice and shattering it along with a section of the monster's 'mask'. "Thundaga!" The lightning bolt struck the heartless's new weak spot dead on. Scan told Kairi it was nearly finished by now.
It swung it's claw, but Kairi was prepared. "Reflaga!" she cast the barrier in time for the claw to slam into it. It burst, damaging the heartless that much more as it staggered. To end things, Kairi focused. She summoned a devastating power into her Keyblade with the help of her new Link and activated her Shotlock. She jumped into the air, summoned a dozen pearls of pure light, and rained them down onto the heartless.
It was overkill, to be perfectly honest. Kairi would later admit that if she wasn't high on her Link, she would have probably found a calmer way to dispatch the heartless. The results were undeniable either way. Kairi stood victorious, Ruby was safe, and the beast faded away. A large crystalline heart floated shortly into the air, before vanishing into the ether.
"Woah..." Ruby was entranced by everything she had just seen.
Kairi felt her Link fade, and frowned. She likely wouldn't know who she connected with now, not unless she met them or managed to connect again in the future. Oh well. I should finish my job before another strong heartless appears.
Kairi looked to the Keyhole once more and raised her Keyblade. Ruby watched as even more light gathered at the tip of Kairi's weapon. It fired a beam of solid white into the strange Keyhole. There was a flash of light and a locking sound. The Keyhole disappeared, leaving behind only a keyhole-shaped indent in the rock face. "What was that!?" Ruby asked loudly.
Kairi looked back to Ruby and sighed as she remembered the situation her stowaway had built for herself. "That was my mission," Kairi answered. "Which means… it's time to take you back home."
The realization dawned on the young girl as well. "Uh oh..."
"C'mon," Kairi reached for Ruby's shoulder, "we need to get going, the sooner the bet..ter…" As her hand came to rest on Ruby's shoulder, Kairi felt something that answered her questions. A pulse between the two of them, faint but existent. "It was you..."
"What was me?" Ruby asked.
"The Link… I connected to you," Kairi realized, "to your heart."
"To my heart?" Ruby asked, "What's that mean?"
"If it means what I think it means..." Kairi answered, "then it means things got a lot more complicated."