Ryuunosuke Uryuu  

, 雨生 龍之介

Ryuunosuke, who serves as the master of caster, is a murderer who uses blood from a family he killed for the ritual to summon this servant. despite not being a magus, he was chosen by the holy grail war to fulfill its requirement of having seven masters and seven servants. although ryuunosuke lacks knowledge about magic or the fourth war, his role in it is solely to observe caster's killing spree as a form of entertainment.