Part 1: A happy moment or two
Though their shared title had changed from "siblings" to "couple", little changed in the relationship between the magus of swords and the white-haired homunculus. Every morning Taiga still brought Illya to the Emiya manor for their morning meal and every weekend the pair would go out and do things together, much as they had done that fateful weekend so long ago. All of this was Illya's conception of what it meant to be in a relationship with someone. In this ideal derived from her what few memories she held of her mother and father interacting and tempered by the deep feelings for Shirou, Illya had finally found the happiness and companionship she had longed for all those long, cold, nights locked in her family's snow-bound castle. However, In her new-found happiness, Illya ignored another factor that would soon come to decide her fate. Even in these brighter days, her artificial life ticked ever closer to it's end as her body finally consumed what little mana she had leftover from the endless well that was the True Grail. Now, with little power left to fuel her existence, illya stood unknowingly at death's door, with only a slight sluggishness of her mind and body to remind her of what terrifying fate awaited her in the near future.
And so Shirou, the source of Illya's happiness and the one who she now referred to as her "boyfriend", much to Sakura and Rin's annoyance, continued to wait in silence for Rin to eventually bring him the news he had waited so long to hear. However, as the days and weeks past, no good news passed from the lips of Rin to Shirou's ears. The myarid of magical texts stored in the Einzbern Castle vault provided little solace save for what they had already known, homunculus such as Illya were fated to die young. It was simply a facet of there existence as artificial humans. In creating a being that more a container for the Grail then a person, homunculus were never meant to live as humans did. Those who did gain such emotions, such as Illya and her mother, were aberrations whose existence were made ever more painful in that they would be snuffed out so soon. All of this, while not new knowledge to Shirou, lay on his mind even in those happy days he spent with Illya and his other friends. It was all happening again, he imagined in anguish. Just as Saber had left him following the Grail War, Illya to would soon be spirited away from him and there was not a single thing he could do about it. Though, like his small partner, everyday for Shirou since their shared confession had been happy and full of hope, the fact that he could not save Illya not matter what he did was always at the back of Shirou's mind. And so, he placed what little faith he had left in Rin and hoped for the best.
Part 2: A hero's resolve
One day, in that strange time between the end of the school day and the time when one finally arrived home, Rin confronted Shirou at the their high school's gate. She wore a grim look upon her face, a visage that spoke volumes of the ill nature of the news she had to deliver upon the red-haired magus. Placing her right hand upon Shirou's shoulder, as if bracing him for something, Rin did her best to speak without upsetting her friend.
"Emiya-kun..." She spoke turning her head to the side as if trying to avoid showing the anguish hiding behind her eyes.
"What is it Rin? Did you find anything that cold help Illya?" Shirou replied in a manner meant to hide his fears of the worst possible news.
"I did and I didn't." She said with a sigh. "Do you want the good news or bad news first?"
"The good..." Shirou trailed off, hoping something, anything, of use could be gleaned from the endless stacks of books in Illya's ancestral home.
"I've found something we can do to fix the problem of Illya's dwindling mana supply." Rin spoke in a matter-of-fact manner.
"Then what's the bad news?! This is great!" Shirou's desire to hear any good news quickly overrode his commonsense.
"We can only do this if we allow Illya's current body to perish and then transfer her spirit to an artificial body. I know a magus in England who creates such things, though she charges quite the steep few for her service, and. I imagine that I can procure the funds for the ritual by selling all of the tomes I've rescued recently" Shirou's will nearly broke in two upon hearing Rin's words. Even if it meant saving Illya's life, seeing her, a girl he called both his sister and partner over the course of the last year, die before his very eyes was an event so painful he couldn't even imagine it properly. "If you can accept the fact that you'll have to watch Illya die in order to save her life, then yes, we can save her." Archer had once said that being a hero meant saving yourself just as much as it meant saving others. Shirou, upon hearing Rin's plan, finally knew what he meant. If he was to save Illya, a girl he had come in the last few months to care for more then anyone else, he would have to overcome the fear of losing her. This was not the same circumstance as parting from Saber, here and now he could do something. Even if it simply meant finding the strength to endure the pain of parting with Illya as she was now. Standing in silent contemplation for several minutes, Shirou finally resolved to do all he could to save someone he loved very dearly.
"Tohsaka, if this will save Illya from leaving this world, I am willing to do whatever it takes to see things through to the end." Being like this resolute, even in the face of overwhelming odds, was what it meant to be a true hero. Shirou imagined.
"Very well then, I have one question for you, Emiya-kun. Do you have any preferences as to what type of body you'd like Illya-san to have? As her boyfriend I imagine you'll be the one who cares most about such an issue." And so, with a single question, Shirou's iron resolve was broken down and replaced with a sense of panic.
"W...wait, I'm just going out with Illya to make her feel better until we could find a way to help her. Now that we do I don't think I'll need to keep this up after she is ok again." Shirou's denial was half-hearted at best, allowing Rin many openings in which to pierce a thousand and one holes in his argument.
"Come on! You talk about Illya-chan in exactly the same way you did about Saber around the time you two went out on that date. Deny it all you want, your in love with her." For the second time in only a handful of minutes Shirou's mind reeled. "But if your going to keep saying other , I'll just base Illya's new body on the pictures of her mother I found tucked away in the some of the books I was reading through. Here, take a look." Rin then abandon Shirou for a moment to rifle through her bag for the picture in question. After a moment she produced a glossy, though faded, shot of a tall, snowy-haired women, with the same piercing red eyes Illya possessed. Her smile was dazzling and her body the perfect image of what Illya may have looked like if she had been given the chance to grow up like a normal girl.
"She's beautiful..." Shirou muttered while pouring over the picture with his eyes.
"I will take that as an yes then, Emiya-kun. I will speak to you again when I have everything together. Till then, please take care of your little girlfriend." Taking the picture back, Rin walked off with a joyful wave and a smile on her face. Convincing Shirou was the easy part of the plan, after all she knew he would never back down from helping a friend in need, the ritual, with all its magical issues, would test her mettle as a magus to it's limits.
Part 3: Ritual of Bonding
By Rin's estimate Illya likely had one week to live before her body would consume the last bit of mana left in her tiny frame and she would slide off the mortal coil and into whatever afterlife awaited creations of magecraft and sorcery. Shirou in turn did his best to make Illya's last week of life a good one, spending every moment he was not in school or at work with her. It was what he had promised to do, not only to himself, but to Illya and Rin as well. Illya, despite her actions during the Grail War, was a friend to everyone within the makeshift Emiya family and her death would sadden more people then then tiny homunculus could ever imagine.
And it was during that week that Shirou contemplated the other claims Rin had leveled against him the prior week, she had said quite clearly that she firmly believed Shirou was in love with the girl he had been pretending to date for the last few months, and, he thought, she was quite right. Shirou had always thought of Illya as a younger sister, someone he had to protect. Or at least, that was the state of his view of her up until a few weeks ago, in the present Shirou no longer knew what to think of the white-haired girl with whom he had spent day after day as of late. Though she was often crass and annoying, Shriou found Illya was charming in her own way. She was nothing like the servant who had stayed by his side for those fateful two weeks, but she still occupied a similar place in Shirou's heart. When he was with her Shirou was finally able to put aside the pain he had felt upon Saber's returning home, though no one could ever truly replaced the King of Knights, Illya had made it possible for Shirou, in small ways, to move on with his life. He did love her as more then a sister, though what that exactly meant would have to wait until Illya's life was no longer in a state of flux.
The fated day fell on a Saturday. Illya, nearly unable to move the night before, had personally requested to stay at Shirou's home. Taiga, even without knowing the truth of the situation, could tell Illya was needed her elder brother more now then ever and quickly led her to the home of the one most beloved to her. In her weakend state even speaking had become an issue for Illya, leading her to only being able to utter a few words before succumbing to the allure of slumber. And then, as bed time drew near on the Friday night and Illya lay sleeping in Shirou's room, Rin swiftly sneaked into the Emiya manor with a strange object in tow and met Shirou at the buildings front gate.
"Tohsaka..." Shirou said with a yawn. "Did we really need to do this tonight? I'm barely awake as is."
"Time is not on our side, Illya will certainly be dead by morning and if we don't act now her spirit may pass on before we can coax it into this..." Rin made a grand gesture as she pointed out the manikin-like object sitting at her side. "This is body my magus friend made for us, she did a extremely good job with it. Though I had hoped she would concidering the ridicules sum of cash I paid her for it." The manikin was a carefully constructed portrait of Illya's mother though styled in such a way as to take in account the small differences between Illya and her dearly departed mother. Shirou merely nodded in return and helped his fellow magus carry the artificial body into his home. By then it was midnight and, as Rin could barely sense even with her grand knowledge of all things magical, the mana Illya had been leaking all this time had finally stopped flowing forth from her small body. There was little time, the window in which Illya's spirit could still be bound to a new body would soon pass, a fact that caused by magi to run, artificial body in hand, to complete the ritual as soon as possible. To save Illya in time, the pair tore through the Emiya manor as quickly as their feet would take them. Knocking over vases and cutting corners with all the speed of a marathon runner in their prime, so dire was the situation at hand as to require such haste.
Finally entering Shirou's sleep quarters, Shirou roiled in horror as he saw Illya's limp frame spread out across the bedroom floor. Neither moving nor breathing, Illya was nothing more then a empty husk while her spirit was set free to meet it's fate in the great beyond. "EMIYA!" Rin yelled at the top of her lungs while propping the pale frame of Illya's new body against a nearby wall. "You try and talk to Illya while I prepare the body for transfer. Your the only one who can do this now!" And thus, without a word to his companion in this scheme, Shirou stood over Illya's unmoving form and shouted aloud his feelings. Despite the fact that he was speaking in no particular direction nor at anyone in kind. Shirou felt a warm presence embracing his very soul. It had to have been Illya, he thought, and as such his words feel upon formless ears.
"Illya, I had hoped it wouldn't come to this but even if your body is unable to move. I still don't think it's your time to go! Just think of all the things you haven't done yet, all the places you haven't seen! But, more then that, think of all the people who would miss you if you were to go now. Your everyone's beloved little sister, without you Taiga-nee's life would be so boring and breakfast just wouldn't be the same without you." As Shirou spoke Illya's essence held firmly to his heart, producing a warm sensation akin to that he felt as Illya had insisted on wrapping her tiny arms around his waist every night as they slept in this very room. Meanwhile, Rin did her best to prepare Illya's new form for the transference of soul. Carefully etching rune after rune onto the night hair and chanting line after line of an obscure rite she had only learned from text known only to a handful of magi, Rin had managed to complete her end of the plan. All that was left was for Shirou to coax Illya's errant spirit into her new body. It was entirely up to her if she wished to stay in the material world or move on, but it was Shirou's job to give her a gentle push towards the former. "And, I'd miss you more then anyone. These last few weeks we've spent together have been great and I hope we can have so much more time like those together in the future! When I was around you I forgot all of the troubles of the past and was able to look forward again. I guess what I'm trying to say is...." he paused, drawing in enough breath to convey such an important sentiment. "I love you and I don't know what I'd do if you were to go now. If you can't stay for yourself, please, do it for me. I don't know what I'd do without you."
For a second, Shirou could no longer feel the warm of Illya's spirit around his heart. Fearing she had truly passed on, the magus of swords couldn't help but shed a torrent of silent tears for his seemingly lost friend. Then, a few moment's later, a noise could be heard from the dark corners of his room. It was the sound of someone trying to raise from a seated position, and failing miserably at it. He had imagined it was Rin, rising from her ritual work, but the gem magus had fallen unconscious after expending so much mana preparing the proper bindings for Illya's spirit to take home in her new body. And again, a sound emanated from that dark corner, this time that of someone standing and stumbling all at once. With Rin out, it could only be one person and mean only one thing...
Quickly dashing across to the offending corner of his room, only to see a the artifical body standing, though with quite some difficulty, on it's own. "Illya, is that you?" Shirou questioned while offering the newly mobile person his hand. And in return the nameless girl took his hand, though she did not speak a word, she didn't need to. Shirou knew all to the warm radiating from her frame, there was no one currently in this world who could make him feel this way... The ritual had done it's job, the stumbling girl before him was none other then his Illya. Though wrapped in artificial flesh constructed of mana and gods know what else, it was still Illya. And because it was lllya, Shriou gently spun her into a strong embrace, wrapping both his arms around her newly minted form and placing a longing kiss upon her ruby red lips. The cathartic release of weeks of worry and hopeless despair, the entwinement of forms last for several minutes, before both parties broke their dance out of exhaustion and sheer relief. Without warning, Illya finally spoke.
"I'm home, Shirou...." Illya said smiling through her sparkling teeth. Despite her complete lack of energy her words were full of love.
"Welcome back, Illya." Shirou said in turn, gently lowering his beloved into her usual sleeping space. It had been the longest week of his life and all had turned out for the best. The future was shrouded in mystery, he imagined, but Illya's place in his heart was no not. He very well knew what he felt for the princess of Einzbern Castle. But, for now, those all he could think of was sleeping away the last bits of anguish brought on my such a eventful night. Laying beside Illya's reborn form, Shirou pulled a blanket over the both of them and planted one last kiss upon her cheek. "Good night...." were the only words he could manage before escaping into night's embrace without a care in the world.