Emiya Shirou has been branded with a Slave Crest. Violation of the terms set by the owner will result in extreme pain. Please do not violate the terms.
Of course, there was no mention of what those terms were. Or how and why he had been branded with a Slave Crest in the first place. Though, considering the situation, he could hazard a guess…
All around him, people, demi-humans, filled the cages that lined the room, and only demi-humans. All of them were either weak from a lack of food or illness to varying degrees. Ironically enough, he himself appeared to be the healthiest. Considering this, the strange Magecraft he suddenly had access to, he could only come to the conclusion that he had been kidnapped and experimented on by a Magus. Kiritsugu had always said that most Magi were an immoral lot. That would explain the new Magecraft and the extra appendages. That still didn't answer where he was, though.
He'd tried asking the girl in the cage beside him in order to confirm his theory and ask if she knew where in the world they were, but… she had simply given him a strange look, opened her mouth and, to his ears, had spoken gibberish. His heart had sunk when he realized that she, and no one else in the room he'd later found out, spoke his language. Hell, he didn't even recognize the language the other slaves had been speaking. Not Japanese. Not English. Not French. Not German. Not Dutch. Not Spanish. Not Greek. The language they spoke was so odd and foreign to his ears that he had a fleeting thought that it must have come from another world…
…Or maybe I'm the one that has been transported to another world?
Before he could give the shocking idea much consideration, a man stepped into his field of vision. He was a short, stout and fat man, wearing an expensive looking suit with long coattails. The man had a devilish grin on his face as he twirled his moustache and adjusted his monocle with the other like one of those cheesy villains from one of those old spy movies from Britain that Taiga had made him watch once.
Shirou instinctively knew that this was the man that applied the Slave Crest to him. In other words, this was his, and every other person in this room… owner… his stomach churned.
"Oh, it seems our surprise acquisition is awake. Yes," the man, the Slave Trader, said.
Shirou glared at him. Even before the Slave Trader had opened his mouth, he'd felt an instinctive burst of disgust for the man. Not that it mattered what the man said. Like the rest of the people in the room, he could not understand the foreign words of the Slave Trader.
"Hmm, it seems this one has some spunk. Yes," the Slave Trader's grin widened. "Good. You're going to need it. Hehe."
Shirou shivered at the Slave Trader's giggle. Again, he could not understand the words, but the man's gleeful expression was enough to clue him in on the fact that, whatever was going to happen to him next, he wasn't going to like it.
The Slave Trader snapped his gloved fingers. In response, two massive, muscle bound men wearing a blank mask appeared. "You, prepare the slave. You, gather the others and prepare the ritual. Before we can sell this product, we must first make it usable."
One of the masked men disappeared with the Slave Trader, while the other opened the cage and stepped inside. Shirou was about to start resisting whatever the man was going to do, but the moment he began to move, his Slave Crest acted up and stopped him with a sharp lance of pain.
"Argh!"
Shirou gasped, collapsing to his knees as the Slave Crest flickered with a vile purple light, his entire body locking up. This was what it felt like to be electrocuted, he'd imagine. The pain was so intense that he could scarcely breath, and it immediately put a stop to even the idea of trying to resist. Even the act of making a Circuit fell woefully short to this level of pain.
A rough hand seized him by the shoulder, digging into his flesh, and forced him on his feet in spite of the pain. He was unceremoniously frog-marched out of the room, through several doors and, once they had reached a small room somewhere in the back, was shoved to the ground in the center of the room.
Right in the middle of a massive and intricate Magic Circle carved into the floor.
Heart pounding, Shirou scrambled to get up and move out of the Magic Circle. From what little his father had taught him, he wouldn't want to be caught dead anywhere near a Magic Circle, but…
"Don't move," the masked man ordered, and, even if he didn't understand the words, the Slave Crest forced him to comply with another sharp burst of pain. He could do nothing but stand still in the center of the Magic Circle, forced to wait and see what was going to happen.
"Now then. Yes," the Slave Trader reappeared, accompanied by another half a dozen masked men. He stepped in front of Shirou as his men began to circle the Magic Circle, surrounding Shirou on all sides in what was clearly the beginning stages of a ritual.
Shirou's heart was going so fast that it was beating a permanent tattoo against his chest and his tail was swishing behind him in unease. What were they going to do to him?
"Let's begin. Yes," the Slave Trader twirled his moustache as his men began to fill in the groves of the Magic Circle with some kind of viscous liquid. In a matter of moments, the Magic Circle had been prepared, and when the masked men began to chant, the Magic Circle lit up with bright light. In a few moments, the ritual would commence.
I guess you forget Powerstone.