She was the first.

The reason I was in Sabra la Tau to begin with was to save the second. By the time we won, and Ptou mended what was left of her soul, her body was hours from giving out. She was three years younger than you are now.

I don't really understand how contracts work in Saber and Archer's world. But if there was any doubt at all, anything other than absolute certainty... I'm never going to lose someone to that again, if I can help it.