Uryuu Ryuunosuke (雨生龍之介, Uryū Ryūnosuke) is the Master of a Caster class servant in the 4th Holy Grail War.
He is a cruel man that's only interested in killing people. He thinks that humans can only guess the essence of death by observing other people's death, and make up a virtual experience, so that's why he became a murderer. According to him, claims that depiction of cruelty in fiction has a bad influence on young people are ridiculous nonsense, because if blood and screams in splatter horror had been at least a little more realistic, he wouldn't have become a homicidal maniac. He is satisfied by squeezing the best out of the life force of those he kills, of feelings such as the attachment for human life, anger and affection. To let his victims know the exact time and circumstances of their death, that in itself had a deep meaning as rich as a miniaturized life and the more he killed people, the more he understood the lives he took. That knowledge, that discernment in itself was a kind of dignity, a style that in his distorted logic, he considered as something "cool".