It took a serious effort to force any sort of speech out of his body, but he managed it anyway. "Who are you? What... what was all that?"
Sakura sat back and stood. "I'll go get you something to drink, Senpai."
Shirou closed his eyes as he heard her slide a door shut behind herself. He knew how his house's doors sounded, but why would they have taken him here, rather than to a hospital?
"You may call me Caster. The rest... some centuries ago, several mage families came together and carried out a ritual in an attempt to revive an old form of sorcery - you're familiar with the difference between that, 'mahou', and 'majutsu', magecraft, correct?"
"...yes."
"So. Anyway, it was only partially successful - what they ended up with was capable of most of what they were looking for, but could only be accessed for brief periods, and then only after repeating a simplified version of the original procedure. Which has been happening periodically ever since.
"The way the current version works is that the, er, incarnation of this sorcery, what's called the Holy Grail, selects seven magicians in all the world, usually from specific family lines, and allows them to summon a single, tremendously powerful servant spirit. Then those seven pairs fight each other until only one survives, to whom the Grail then reveals itself and allows them to - briefly - utilize its power."
"You and... that man... you're..."
"#Bingo.# You're quite right - I'm a Servant. And I can tell you that all this is relevant to your life beyond the obvious reasons because one of those traditional families I mentioned is the Emiya clan. Even if you choose not to take part in the Grail War, most of the other parties will see you as a threat and... take steps."
"But... I can't. I'm not a mage."
"Talent matters, for this. Training doesn't. My Master knows even less than you do, as it happens."
But, Shirou thought, trying to figure out how to phrase it aloud - or even if he wanted to,that would make me your enemy... He had recovered enough to twitch in surprise at the snap of the door opening.
"Shall I help you with that, Nishi-sama?" Caster asked, and there was a slight creaking from the tatami as though his weight was shifting.
"No," Sakura said softly, "I have it, thank you."
...Oh.
Incidentally, I'd been thinking further on the 'preserving threat levels' front, and perhaps one of the association mages - or other competitors, or even Medea - has a way to steal Reiju? And, with them, Ilya's control over Berserker? If she retreats after her first attack starts going badly, then gets jumped before she can recover...
If that does happen, and it turns out to be Medea, it won't neccessarily mean that she doesn't have Archer-S in her pocket, too - I have something in mind that'll give her mana to burn...
Ja, -n
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"Puripuri puripuri... Bang!"