Disclaimer: I do not own My Hero Academia or Fate/Stay Night

...

Rin took steady breaths as she considered the Servant in front of her, and wasn't that a difficult idea to get her head around. It had been decades since her brief encounter with Rider but she still recollected how easily she could have been killed if Shirou hadn't been there. Since that all so brief battle had been their only time in confrontation with the Servant of Shinji Matou, they had never been able to deduce just who the hero of ancient times was. That, unfortunately, made it difficult to judge just how she should go about this situation.

She really felt sorry for anybody who got in the way of the coming conflict. Rin had essentially done her initial move to make a statement; to tell all those who were smart enough to not throw their lives away, that fleeing was a far greater choice than getting anywhere close to her. Now however, now she had to get serious.

Rin simply hoped those who had gotten her initial message had run as fast as their legs could take them.

Initiating the first move, the ground in front of Rin began to burst, as scalpel sharp stalagmites erupted from the surface in a blistering fast wave towards where Rider was standing. At a speed faster than most humans could comprehend, Rider pushed off the ground mere moments before she was impaled and leapt onto a nearby roof. The footing beneath the Servant however melted away, the tiles turning malleable in texture in an attempt from Rin to ground the Servant in a singular place.

It did little as Rider leapt off the swiftly altering surface before she had gotten truly caught. High in the air, Rin tried to keep track of Rider however had to shield her eyes as the Servant had altered her trajectory so that Rin was blinded by the sun. Rin knew this tactic however and swept her hand to the side, a shimmering golden light erupting in front of her which protected her as Rider's nail collided with it in a shower of sparks. Rin watched as the nail shuddered in its position, as if still trying to penetrate her defence after having been stopped.

Her attention on the weapon almost cost Rin as Rider landed atop the shield she had created, seemingly unfazed by the attacks that had been set upon her thus far. Rin willed her shield to move about freely outwards becoming spherical in shape as she tried to capture Rider once more. Again though the Servant leapt clear before falling to Rin's clutches, vaulting over Rin and away from the dangerous stalagmites which littered the road to the train station.

Twisting on the spot, Rin raised her hand and fired off multiple shots, Gandrs whipped through the air like bullets to which Rider merely batted them away with the nail in her hand. This however was not the intent of Rin's attack as the world around them began to grow dark, black clouds filling the sky where there had been only blue stretching on as far as the eye could see. It took only a handful of seconds for the sun to be completely blocked out.

Any watching had to cover their ears and shut their eyes tightly as the lightning crashed through the air. Rin was one such person, having not wanted to rupture her eardrums with the deafening attack. When she did look back however, she saw Rider standing there, completely unharmed. Before she could try to reason how Rider had avoided the lightning strike, the Servant's weapon crashed to the ground, Rider having tossed the nail and chain high into the air to act as a conductor and leave herself untouched.

Rin couldn't help but allow a sigh to escape her lips as she reinforced her body. She should have realized beforehand that it wasn't going to be that easy.

...

Re-Destro wasn't sure whether to be grateful or not for this intrusion into his carefully laid out plan. Rin had been strong, unexpectedly so but everybody had a weakness. Or at least everybody should have a weakness. Chances were that whatever weak point Rin had she guarded it as carefully as she did the true extent of her powers.

Reshaping the town on a whim.

Crafting winds strong enough to turn buildings to dust.

Summoning lightning down on what had been a beautiful sun filled day only four minutes ago!

Re-Destro found himself rubbing at his eyes with his forefinger and thumb, weariness filling his body. How could someone so powerful be so content with taking a background position in life?

Then there was the question regarding the person fighting Rin. While Rin they had some manner of intel on, wrong or not, this new person was an anomaly that they hadn't considered. While her offence hadn't been all that great as of the moment, she was keeping herself out of harm's way. It seemed as if she was just feeling out the level of threat before her and when she had all the information she needed she would act accordingly.

The only real thought crossing Re-Destro's mind regarding this woman's origins was that she was a bounty hunter, as ridiculous as that sounded once he had clarified his thoughts. Whether or not his theory was true or not, what was true was that with her having stepped in it had given him and Skeptic time to issue the retreat for many of his forces. Having witnessed people getting sucked up into Rin's vortex, there had been no point in sacrificing more lives than necessary. Now though having witnessed the small clash between these two women thus far, only the strongest of their forces would have a chance and even then, to what point and purpose?

Were Rin to come out victorious but unable to properly defend herself, the image of a mob ripping a fallen foe from limb to limb would garner no benefit for their cause. Were this other woman to walk away victorious they gained nothing from it, the masses having been brought to their knees only for someone far stronger than them to step in when they were unable to do the task on their own.

The only bit of footage that they could realistically use in any sort of way was the initial scuffle between whoever that swordsman was and the first wave of attackers. While it couldn't be used to recruit new people to their cause, it would serve as a good reminder that even if the members of the Meta Liberation Front had trained a great deal it didn't mean they were able to combat someone with years of experience as a trained killer.

Focusing one more on where the two women were fighting, he merely wished that they wouldn't destroy too much more of the town as they attempted to kill one another.

...

Rin bounced off the ground before adjusting herself to land on her feet, the shoes she was wearing skidding across the road before she came to a stop. In front of her Rider was charging forward with her nail poised behind her, primed to strike. Rin made some quick hand movements, drawing an incantation with each index finger before unleashing twin torrents of flame towards her opponent.

The inferno engulfed Rider momentarily before the servant burst out to the right, her hair, skin and clothes burnt from the attack. If the Servant however felt any inkling of pain they did not show it, keeping their face a stoic mask. "Alright, I think I'm beginning to understand," said Rin as she rolled her neck from side to side. "You're not going to stop, regardless of whatever pain you feel, whatever torment you suffer, you will not cease until your goal is accomplished."

While she may have been speaking to a statue, Rin felt it good to voice out her thoughts at the moment as she reached behind her back and beneath her coat, her fingers gripping around the handle of the weapon she had brought with her. While she hadn't thought such an item would have been necessary given her illustrious skill set but she knew that it was better to be overprepared than under.

Now she just had to get close enough to deal with Rider once and for all. She did have one idea but she was going to immediately regret it and if Shirou ever learnt about what she was about to do, she would never hear the end of it.

With her outright hand, Rin summoned forth another torrent of fire, the blaze ripping through the street towards where Rider was standing. The Servant wasn't going to be caught by the same attack twice though, stepping towards the side before sprinting forward so fast it looked as if she was gliding across the road. Rin watched carefully, knowing she had to time this well in order to not suffer any lasting damage. When Rider poised herself to strike, Rin didn't bring forth the golden shield she had before, nor did she leap out of the way.

The nail Rider held pierced through Rin's stomach, the magus gritting her teeth together as she gripped on to Rider's hand, reinforcing her hold with all the mana she could muster. While Rider continued to show no emotion to what was happening, Rin pulled forth the dagger which she had brought along with her. With Rider stuck in place, Rin plunged Rule Breaker into Rider's chest.

This got a reaction.

A primeval scream erupted from the Servant, tilting her head upwards to wail to the heavens themselves. Rin watched intently as the woman before her began to mould and change. Her hair shrunk and changed colour and the complexion of her skin darkened. The structure of her face changed as the visor across her eyes cracked before shattering. The nail embedded in Rin's stomach dissipated into blue glimmers of light before vanishing completely. The magus immediately set about the task of knitting her wound together, the flesh stitching itself up before too much blood spilled from the injury.

As the body of the girl fell to the floor, no longer having any resemblance to the Servant of Shinji Matou, Rin allowed herself to breathe a sigh of relief, returning Rule Breaker to its previous position. Finally, after having exhausted a good chunk of her resources, the battle was over. One thing was for sure though, given that the Rider she knew had been beaten to death in close combat, this phantom Servant was likely far stronger than what had originally been brought forth in the Grail War.

"So, you want to tell me what all that was?" asked Stain, walking forward with Curious' leash still in his hand. Temporarily he looked at the amount of blood that had spilled from Rin's rapidly closing wound but knew better than to try anything foolish. Just because she couldn't move didn't mean she would lose the capacity to call forth something to tear him limb from limb.

"Hypothetically, it was a possession," said Rin. "Somebody or something was using that girl's body as a host to bring forth a heroic spirit from a time long since past in an attempt to kill me. I have several theories on how this came about but will need time to get some conclusive proof."

For several seconds Stain remained silent, contemplating what it was that Rin had said. First and foremost he focused on the fact that Rin had said 'kill me' as opposed to 'kill us.' To him, it meant that this had been a targeted attack. Had Rin been expecting somebody to eventually come after her? Was this an individual incident or would there be more to come?

He had been able to watch the fight for the most part, having trained his body to the limit. Witnessing the purple haired woman move at the speed she had and knowing what he himself was capable of, the battle would have been one where he would have been on the defensive. Could he have gotten a taste of her blood to turn the hypothetical fight in his favor? Who knew.

"Now," said Rin as she focused on the large building in the centre of the city. "Let's go give Tiddles back to her owner."

...

At the start of the day Re-Destro had envisioned Rin and her accomplice kneeling before him, battered, bruised and at their mercy. How quickly things had changed.

"Nice little pad you have here," said Rin as she strolled into his office, still holding onto Curious' leash. Standing behind her was the scarred man, surveying the room as if searching for traps and any more ambush attempts. By all means they had been options but given what he had seen the two of them were capable of, Re-Destro had opted to live another day. If he unleashed all of his rage, he knew that he would have a fighting chance but to what point and purpose.

"That's kind of you to say," said Re-Destro politely. His objective now, if nothing else, was to get Curious back. At least that way this entire endeavour wouldn't have been a total bust. He just wondered what he would be able to offer the woman in front of him in exchange for the life of his high-ranking subordinate and if what he would offer would be equivalent to a human life.

"Here's your Executive back," said Rin, holding the leash out in front of her, offering it to him.

For a second, Re-Destro found himself incapable of figuring out what it was that was happening in front of him. By all means this could be some sort of trap on Rin's part but would he get a better chance to rescue Curious?

"Trust me, if I was going to liquify your organs I would have done so already," said Rin, sensing his uncertainty.

Re-Destro took that at face value, figuring that Rin wouldn't simply bluff that she was capable of doing such a thing. Stepping forward, he reached out and took the lead from Rin before taking several steps back, Curious following him. "If I may be as so bold as to ask, is whatever you did permanent?" he asked, not particularly wanting Curious to remain in this pitiful state.

"It's just a touch of hypnosis, it'll break with a simple snap of my fingers," said Rin.

Re-Destro nodded in understanding. He may have gotten hold of his subordinate but the negotiations were well and truly still afoot. Rin had clearly stated that it would be when she snapped her fingers, so it went to say that it would only be her fingers and no others.

"I feel I should inform you that my terms for her sanity being restored are quote simple," said Rin. "Any sort of refusal and I will have to have Stain here separate your head from your torso. As it so turns out he's more than just a pretty face to do my chores for me."

Re-Destro felt his belief in choosing to instruct his troops to retreat suddenly become far more validated. Again, Rin did not seem like the kind of woman who would bluff in this sort of situation. If the person standing by her side was well and truly the Hero Killer Stain, it spoke volumes of either the level of intimidation or leverage that Rin was able to generate if she was capable of keeping someone of that calibre as her...errand boy?

He felt that it was better not to think about it too hard.

"Firstly, any and all information you have regarding my known location is to be deleted and erased from your mind. Under no pretence are you or those who serve under you permitted to seek me out for any reason and you will not send others on your behalf to my location. To do so will result in the complete and utter destruction of this city and all those who reside in it. I hope you understand very clearly my instructions and will act accordingly. Finally you will have your men organize five briefcases, each with one hundred million yen inside. I hope I don't have to remind you what will happen if you or your associates try to rig one of the briefcases to injure me in any way."

"I understand," said Re-Destro, nodding his head lightly. Five hundred million yen was a significant sum and would leave a dent in the Meta Liberation Army's finances but he knew that to deny the woman in front of him would prove more costly.

"Well then, get to it," said Rin as she plopped herself down on one of the office chairs, crossing her arms across her chest. Stain remained standing, his eyes still darting back and forth as if expecting any kind of attack to assault them at a moment's notice.

Re-Destro couldn't help but sigh as he reached into his pocket and pulled out his phone. This was going to be a very expensive phone call.

It didn't take long for everything to get sorted and not more than twenty minutes later, five silver briefcases were lined up at the elevator door. Rin watched as Stain opened each of them one by one to ensure that there was nothing malicious hidden within them. The Hero Killer gave Rin a curt nod, one which was swiftly returned by the magus before she pressed the elevator's button, opening the doors to the path down.

"Well, with that I believe our business is concluded," said Rin as she picked up one of the briefcases, leaving Stain to clumsily handle the other four. The two of them stepped into the elevator before Rin lifted up her spare hand and snapped her fingers together. "I do hope we never have the pleasure of meeting again."

As the doors to the elevator closed and Rin and Stain made their descent, Re-Destro reached down and undid the collar latched around Curious' throat, the woman seemingly waking up from a trance, confusion etched across her face. As she struggled to find any words to say, Re-Destro took off his jacket, draping the object over Curious' naked body.

"Re-Destro?" she said softly, slowly recognizing the location before her and the person acting kindly towards her.

"I'm here, it's okay," said Re-Destro calmly.

That was all Curious could take before tears began to swell up and she began to openly weep, clutching the jacket tightly across her body.

...

Rin sat on the train, chewing at the tip of her thumb as her mind raced through what she had encountered on her way to return Tiddles. Rider. A servant from the Holy Grail war. Why here? Why now? Who had possessed that woman with the power of a Servant? Was Rider always that powerful?

Strangely enough, she was already coming up with theories regarding all of those questions.

The here and now unsurprisingly linked in with one another. It had not mattered where she had lived since having come to this world, the first thing she had done was set up protective wards around everywhere that she would conduct her magecraft. The unit she had shared with Shirou, U.A and the scope of the building she now had set up as her workshop. Included in those wards were sigils to prevent detection from outside sources. She hadn't been targeted thus far because she had only used minimal magecraft outside of her wards.

Today had been the exception.

The other two questions were more difficult to get her head around. Back when they had prepared themselves to combat Rider during the war, they had found Shinji's summoned warrior beaten to death, the culprit being Souichirou Kuzuki, Caster's Master. Souichirou had been a trained fighter and his blows had been enchanted with Caster's spells and if he was able to defeat Rider with ease, it did give her some indication of Rider's strength.

Which was nothing like what Rin had encountered today.

So, that then asked whether or not the being who had possessed that woman had increased their strength to a level where she would pose a threat to Rin? Did they know just what Rin was capable of? To be able to make Rider react as quickly as she had when the ground had burst forth or lightning had...

So that was it.

Rin rubbed at her eyes as she came to her conclusion. It made sense given how quickly Rider had been able to adapt to magecraft which affected the environment but had sensed no danger from Rule Breaker. Rider had been tuned in with nature, ridiculously so.

She needed to get in contact with Shirou immediately. There was no telling what danger he could bring forth from one of his little escapades through the night if he decided to bring forth some real power.

Little did she know that Shirou was currently a lot closer to where she was heading than she realized, having been sent to Yokohama hospital to receive surgery on the wounds he had received. The hospital itself was only a couple of blocks from where she had set up her workshop.

The town itself was also about to become the sight of a battle on a scale not seen in many, many years.

...

Hope you enjoyed.