Nowhere to Go
(Back in the Emiya estate, guest room)
Watching Seiba sit up and look around the room and at him in confusion brought back old memories. Well as old as any memories he actually still had, anyway. That expression of there's no way I should be alive, he wondered if that's how he looked upon waking up in a hospital bed after the fire. Since only Emiya Kiritsugu had been there to witness it, and he only saw the man a couple of times before the latter's death, there was no way to be sure. His first trip once out of hospital was his now-father's funeral. It was ironic, he recieved the Emiya's name before even knowing Kiritsugu's.
If only he had known. The fact that Shirou did not remember his own family, even its name - was like a revelation to Kiritsugu, a man for whom his family's name would soon be lost along with his dwindling life. For one who aimed to save others, the loss of the one before him was like a twisted sign. With no other choice, he entrusted the Emiya family name and fortune, such as it was, to the boy without either.
"Saber, how do you feel?"
"Don't call me that, the name's Sasaku," she muttered in wonder. She honestly hadn't expected to regain consciousness, having estimated that using the energy required to heal herself would leave precious little to resist death by Gaia's corrective pressure. However, in the intervening time, she learned or rather -recalled- something important. Gae Bolg had passively forced a curse upon the flesh that it tore through, specifically one that prevented healing. Even though she could theoretically heal in opposition to this, the cost was as mentioned prohibitive.
The fact that it was a continuing curse, one linked to the continued existence of the spear, meant there was another way to tackle the problem. Frowning at the fact that she had overlooked such a detail, Sasaku activated ((Higher Law)) to purge the curse from the wound. The resulting massive expenditure of energy that this took nearly floored her. Actually, she did drop to the floor before Shirou was able to catch her.
A critical mistake. The curse from a source as powerful as a Noble Phantasm, transferred via direct physical contact, wouldn't be removed as trivially as a simple hex or poison. As Shirou gently shook her back to consciousness, she noted that she was now less than an hour from death. Probably mere minutes.
"Stay with me, Sasaku?" he asked as he saw the light return, if dimly, to her eyes.
"Yeah... it doesn't matter," she replied softly after a moment. "Sorry for the trouble."
"You can't just give up like that. I'm here for you," he declared earnestly while settling her back onto the bloody futon. He couldn't see anything physically wrong with her, but of course there was always the possibility of internal damage.
"It's basically over for me. I don't have anywhere to go," she stated without any anger, bitterness, or sadness while explaining her predicament as directly as she could. "The world is about to crush me into nothing."
Those lines stirred something in Shirou's chest. He might have mistaken it for an emotional response, but this was actually caused by Avalon trying to extend its healing effect in accordance with his desire to help someone else. However, he did know one thing about not having a place in the world.
"You can stay here as long as you need." Yes, while the human desire to live was as powerful, it was practically miraculous at times, conversely there was nothing to be done if the girl herself had decided to passively accept. He could practically see the signs of a person preparing for their conclusion, having been there before. He grasped her small hand in both of his. "I don't mind the trouble. Tell me what I can do."
Opening her mouth to deny him, her free hand moved to rest on top of his. She stopped. "You're a Master?"
"What's that?"
Sasaku took a second look at the Command Spells on Shirou's hand, just to be sure. This changed everything, but she had to be quick. "How much do you know about the Holy Grail War?"
The boy only blinked at her, causing the Servant to wonder what the Grail system was up to if someone who didn't even know about the ritual could be brought into it. "The quick version then. Chosen magi, Masters, summon familiars, Servants, and fight for the Holy Grail. It grants wishes to the winning pair."
"That sounds straightforward," he said after a moment. "I assume that means you're a Servant. Ah, so by nowhere to go, you need a Master to form a pair with?"
"Yes." His clearheadedness was quite encouraging, though perhaps simply because he didn't know what the War entailed. Well, few did anyway. She wasn't taking advantage of his ignorance, since the Grail had already given him the Command Seals, which made him a target. "Will you accept my service as your Servant? I will do all in my power to achieve your wish."
Shirou paused before replying. "I will. But I don't know magic, so..."
"Magecraft," she corrected him. "I can take care of establishing the contract. Just a moment, repeat after me the following:"
(A few minutes later)
After the brief ritual (Sasaku said the Grail handled most of the heavy lifting, which made sense), Shirou looked over his new Servant who was once again slumped on the futon. She had warned him that, due to having to supply the mana for the ritual since he couldn't, this was likely to occur. At that moment, she was to him, someone only I can save, just like he was to Kiritsugu. Yes, Emiya Shirou was looking for the one person who only he could save.
As Sasaku had asked him to stay, expecting to recover before too long, he simply watched over her quietly. The color seemed to have returned somewhat to her complexion, but more importantly, as her eyes opened, he could see the power of a will to live shining in them.
"Sasaku, if you don't mind me asking, what exactly is your wish?"
"I'm kind of a foreigner here," she explained after thinking about his question. "For me to return to my home, I would need something on par with the Grail."
"You must have come quite a distance, then." She nodded.
"What about you then, Emiya? You must have quite a powerful wish if the Grail chose you, despite not knowing of magecraft."
"Honestly, I wanted to save the person in front of me." His quick and honest reply made her frown. It actually did fit, ironically. Him becoming a Master and forging a contract did allow her continued survival. "Speaking of which, as a Master, I should be able to do something special right? It wouldn't be a partnership if you did everything."
"You spoke of a miracle earlier. Actually, if you would be willing to lend me your power for, say, tonight..."
.
Notes:
((Higher Law)) is like a flexible self-debuff cleanse skill, that acts on "things affecting me that are undesired". The cost rises with the strength of whatever "debuff" is being removed. The effect is, as we saw, instantaneous which also means no self-limiter to prevent one from killing themselves trying to purge something that they are not able to - since there's no time to react.