Ryuunosuke Uryuu

Ryuunosuke Uryuu is a villain from Fate/Zero who is the master of Caster during the fourth Holy Grail War.

Background
Ryuunosuke is a serial killer. While searching for different, more "amusing" ways to commit murder, he finds a book at his parents' house with instructions on how to summon a Servant. Even though he is not a magus, he was selected by the Holy Grail to fulfill the war's requirement for seven Masters and seven Servants. However, he knows nothing of the Holy Grail War; his involvement in the war is mainly to watch his servant Caster kill people in unique and thrilling ways.

Personality
Ryuunosuke is simply obsessed with the process of death and dying. He believes that humans are inherently curious in death similarly to a sort of forbidden knowledge and try to understand it by observing other people's death while making up a virtual experience, which is why he became a murderer.

According to him, beliefs about depiction of cruelty in fiction having been a bad influence on young people are ridiculous nonsense, because he wouldn't have become a homicidal maniac had it been for blood and screams in horror being a little more realistic. He satisfies himself by squeezing the best out of the life force of those he kills, and of feelings such as the attachment of human life, anger, and affection. To let his victims know the exact time and circumstance of their death, that in itself had a deep meaning as rich as miniaturized life, and the more people he killed, the more he understood the lives he took. He considered that knowledge and that discernment in itself, which was a kind of dignity and a style in his distorted logic, as something "cool."

His last thoughts were the brightness and vibrance of his lifeblood and the excitement as he experienced his own death.