first rate murderer

"If that's the case, then he should have had the goal of retrieving lost holy relics like his father all along. Indeed, Kirei did join the same department as his father in the end, but before that, he was transferred three times and was once chosen as an 'Executor.' He was only ten-something years old then too. This job cannot be done without a certain amount of willpower." That was the Holy Church's bloodiest department, called the Shura's Den for its responsibility of punishing heresies. To be able to gain the title of "Executor" would mean that he is a first-rate murderer, signifying that he has passed brutal and pious training to become mankind's weapon.

- Fate/Zero: Act 1, Part 2