I do not own Naruto or any part of the Nasuverse.
Also, I will be using the anime versions of both series for reference, the English version where available. This version of Shirou is post-UBW, True End.
"Shirou, is the armor really necessary?"
"Yes, Rin, it is." The girl in question released an aggravated sigh as she stood on her knees, a bucket full of pig blood by her side and a brush saturated with said liquid held in her hand. Her long black hair, normally pulled back into a loose ponytail, was now tied into a tight bun so that no stray locks would find themselves falling into the ichor. Before her was a large, half-completed circle of runes and sigils; directly opposite her on the other side of the rather large room was Shirou Emiya, her apprentice/boyfriend/gofer. Beside him was another bucket full of blood and a brush in his hand. Unlike his companion who was dressed in a crimson sweater and black skirt with matching stockings, Shirou was dressed in black pants and chest armor. His arms were covered by a red fabric, along with a skirt around his waist. His head was covered by a black bandana, though a few locks of auburn and silver hair poked out from beneath the fabric.
"Look, Shirou, I know you're upset about what happened last time…" Rin began wearily.
"If I wasn't there, that rabbit would have taken your head off," Shirou retorted, annoyance tinting his voice. "Hell, it nearly took my head off. Who knows what else may come out of this thing once you activate it," he continued, gesturing towards the incomplete magic circle between them.
"Okay first off, we both know that that was an accident," Rin retorted, pointing a finger at Shirou. "Second, I'm pretty sure I've figured out what went wrong last time, so something like that shouldn't happen again." Shirou was not convinced by his girlfriend's reassurances, but he could not think of a response, so he dipped his brush into the blood and carefully began drawing out the runes on the floor. While the man was capable of assembling a couple of very simple bounded fields, he was nowhere near close to an expert on the discipline. However, he did know that this particular array was especially complicated and had absolutely no room for error in construction, so he needed to be extra careful. This magic circle was related to the Kaleidoscope, a magic that accessed and harnessed the power of alternate realities. The power of the Kaleidoscope was mastered by only one person in the whole world, and only three other people could use it in any capacity, including Rin Tohsaka.
"So what is this supposed to do anyway?" Shirou asked as he carefully measured out the angle for his next stroke.
"It's pretty simple," Rin said as she set aside her brush and entered one of her favorite poses when lecturing him, one finger pointed up into the air while her other hand supported her elbow. "Once this field is completed, it will act as a window into the Kaleidoscope, allowing me to observe alternate realities without actively interfering with them," she explained proudly.
After considering her words for a few seconds, Shirou hesitantly asked, "Can anything break through this window?"
"No," Rin replied, "it's more like watching from a TV screen than an actual window. We'll be fine." Finally satisfied with the project's safety, Shirou continued his work without further comment.
The couple had started work early that morning and due to the size, complexity, and sheer attention to detail necessary meant that almost 24 hours had passed before they were finally finished, but their work was not done yet. Next they each drew smaller circles designed to siphon energy from whoever stood in them. Though this array was technically a form of formalcraft, the simplest and theoretically least power-intensive art of thaumaturgy, since it was connected to a Sorcery, it still required a substantial start-up investment of prana, more than a single person could safely supply. Once the two smaller circles were completed, Rin picked up a large box that she had set to one side of the room and began walking through the larger circle, carefully stepping and dancing so as not to smudge or otherwise mar the lines. At certain points, the young woman would reach into her box and place a gem down on the ground. Diamonds, rubies, sapphires and more, each the size of a golf ball and flawless in make, were placed at strategic points in the magic circle. Shirou tried not to flinch at the sight; Rin often complained about how expensive using gems for her magecraft was, and the price of gems of that size and quality was likely exorbitant. Even if he used up all of the modest fortune that his father had left him, Shirou doubted that he could have afforded more than a few of the gems that Rin was using now.
"All right, done!" she said as she hopped out of the circle, being careful not to disturb the carefully-placed gemstones. Forty-nine jewels glittered brightly, bathing the room in a rainbow of color. After she set aside the now empty jewel box in a far corner of the room, she asked, "Are you ready?" At Shirou's nod, they both stepped into their respective circles. As one they took deep, calming breaths, clearing their minds for the powerful magic that they were about to perform. Slowly Rin raised her arm, the magic crest embedded in her flesh glowing brightly. With all the force and authority she could muster, she declared, "Magie, nehmen Sie meine Macht!"
At the same time, Shirou solemnly intoned, "Trace: on." His magic circuits flared and he could feel his internal prana flowing out of his body and into the circle before him. As Rin continued to add lines to her aria, the circle glowed brightly, each gem lighting up one by one. As soon as the last gem illuminated, the entire circle was bathed in white light, bright enough to make Shirou avert his gaze or risk being blinded. When the brilliance subsided, Shirou's eyes widened in surprise at what he saw. Where the circle once was there was now an image of a forest vista. The image was high above the trees and slowly drifting like it was footage taken from a camera attached to a helicopter. It looked like the forest bordered a mountain; Shirou saw no signs of civilization nearby. In his opinion it was a quite relaxing view.
Shirou began to suspect that something was wrong when the drain on his magic circuits did not subside – in fact, it seemed to be increasing. The image flickered and faded into a blank white, glowing ever brighter. The drain on his prana, once merely uncomfortable quickly became agonizingly painful. Rin, who lacked his unusually high pain tolerance, was already on her knees struggling not to cry out.
"Rin…get out of here," Shirou gritted out through clenched teeth. He struggled to stay upright; his legs were already growing weak.
"No!" Rin retorted, the magic crest on her arm pulsing erratically. "I can fix this, just give me a minute." Shirou's whole body felt like it was on fire and his vision was beginning to fade and darken along the edges. Any minute now he would pass out; if he did, then he could not guarantee Rin's safety.
So like the hero he aspired to be, he acted.
"I am the bone of my sword," he incanted. Behind Rin, prana materialized into dozens of sledgehammers floating in mid-air. While such constructs were more expensive to create than swords, Shirou preferred speed over cost in this instance. In an instant the masses of steel shot forward and crashed into the wall behind Rin, pulverizing the stone. Two more volleys and a large hole was smashed into the barrier.
"You idiot, what the hell are you doing?!" Rin screamed incredulously.
"Saving you," Shirou muttered in response. Between the intense glow from the unstable magic circle and his own fading consciousness, he could barely see anything anymore. But he could still barely make out his lover's outline, and that was enough. A shinai manifested before him aimed at the red-clad woman before him. "I'm sorry Rin." The wooden practice sword shot out and planted itself into Rin's abdomen, propelling her through the newly made hole in the wall.
Shirou fell to one knee. The pain he was experiencing was indescribable. For eight years he had used his nervous system as an impromptu magic circuit, an experience that felt like pouring molten metal down his spine every single day. He had even been stabbed by a massive cursed spear that had nearly obliterated his heart. Neither of those instances compared to the agony that he was suffering now. But Shirou's work was not finished; he still needed to patch the hole that he had made so that any backlash would not spill outwards. And for that he needed more power.
"Steel is my body, and fire is my blood." Dozens of swords spontaneously manifested themselves before soaring towards the hole, some lying flat to cover the opening while other buried themselves to the hilt into the hard stone to pin them down. Soon, a thick layer of sharpened steel made a crude but solid patch, sealing Shirou away. At least Rin is safe, the man thought to himself. Satisfied that the woman he loved was safe, he finally allowed himself to succumb to the pain and passed out into peaceful oblivion.
Pain. That was what greeted Shirou when he came to. His limbs felt like they were made of lead and his magic circuits felt like they were on fire, but in a sense he was relieved by the pain. At least if he hurt it meant he was still alive.
The image that graced Shirou's vision once he managed to force his eyes open was not dusty gray granite but a brilliant blue sky marred by a few wisps of cloud. He slowly pulled himself up into a seated position and took in his surroundings. Large coniferous trees towered all around him. He could hear the faint rushing of water, indicating a river or stream somewhere nearby. Between the trees he could see the outline of a mountain. All told, Shirou guessed that he was in the general vicinity of the location that he and Rin were overlooking earlier. He was uncertain whether he should be proud of his girlfriend for successfully creating a portal to other worlds when she claimed it would be decades before she could even hope to attempt such a feat, or dismayed that she had done so in such a violent and dangerous fashion.
Slowly, carefully Shirou got back on his feet. The Kaleidoscope was not a subtle magic, and if this world's inhabitants had any sort of method of monitoring magical activity, then they would likely be dispatching someone to investigate sooner or later. He would not want to be in the area when said investigators arrived if he were at his peak, never mind in his current half-dead state after being unconscious for who knows how long. He gingerly placed one foot in front of the other and began hobbling towards the river. Until he recovered it would be best for him to hunker down somewhere near a source of fresh water and he could feast on fish or wild game looking for a drink.
He should also look into obtaining a different set of clothes as well. Red and black armor was hardly inconspicuous after all.
Let me know what you think.