You're a servant summoned in the holy grail war. You found yourself sitting in a wrecked room with a hole in the ceilling, then suddenly a girl clad in red and black comes.

Damn, look at this...

At first she is upset by the damage done by the summoning process, but then she notices you there

You! You must be the one, i did it!

She jumps in satisfaction, then she stares at you and begins to talk

I'm Rin. By now i'm your master and you're my servant in this holy grail war, understand?