Born December 28, 1967, Kirei Kotomine was the son of Risei Kotomine, a priest in the Holy Church's Assembly of the Eighth Sacrament. Demonstrating high intelligence and diligence from youth, he skipped grades and rose to student council president at the Theological College of Manresa St. Ignacio. Outwardly meeting his father's expectations of piety, Kirei internally struggled with an intrinsic defect: an inability to feel pleasure from conventional happiness, finding fulfillment solely in witnessing others' suffering. This contradiction drove him to extreme acts of physical mortification, futilely attempting to align his nature with societal norms. Seeking normalcy, he married Claudia Hortensia, a terminally ill woman, hoping familial love would fill his emotional void. They had a daughter, Caren Hortensia, but Kirei's condition persisted. He realized he derived perverse satisfaction from Claudia's physical decline and her eventual suicide—an act intended to prove he could feel grief. Her death cemented his acceptance of his nature, leading him to abandon the pursuit of salvation. Caren was placed with Claudia's relatives. Three years before the Fourth Holy Grail War, Command Spells manifested on his left arm, marking him as a Master despite lacking personal ambitions. Under his father's arrangement, he trained with Tokiomi Tohsaka, a magus from a founding Grail War family. During the war, Kirei initially summoned Assassin while acting as Tokiomi's ally. After Assassin's defeat, he formed a contract with Archer (Gilgamesh). Fascinated by Emiya Kiritsugu—a participant whose ideals contradicted his methods—Kirei's actions were heavily influenced by this obsession. Encouraged by Gilgamesh, he embraced his sadistic inclinations, betraying and murdering Tokiomi with an Azoth dagger. He later orchestrated events culminating in Kiritsugu's psychological defeat and the Fuyuki City conflagration. Kirei subsequently became overseer of the Fifth Holy Grail War. He manipulated sorcerer-hunter Bazett Fraga McRemitz into participating as Lancer's Master, then severed her arm to steal her Command Spells and contract. Violating his impartial role, he manipulated Masters, disclosed traumatic truths to destabilize them—such as revealing Kiritsugu's past to Shirou Emiya—and facilitated conflicts for his amusement. He sustained Gilgamesh for a decade by imprisoning orphans from the Fuyuki fire, allowing their souls to be consumed for mana. In the *Heaven's Feel* route, Kirei played a central role. He surgically intervened when Sakura Matou collapsed, revealing her infestation by Matou family Crest Worms feeding on her mana through arousal. He disclosed Sakura's adoption and biological kinship with Rin Tohsaka, leveraging this to heighten Rin's conflict over killing Sakura. Kirei cryptically advised Shirou that if Sakura must die, Shirou should wield the blade—reflecting Kirei's own regret over not killing his wife Claudia. His actions aimed to witness the corruption of pure souls by the tainted Holy Grail, particularly Shirou abandoning his ideals to protect Sakura. Following the Fourth War, Kirei's height unnaturally increased from 185 cm to 193 cm. He maintained a calm, sardonic demeanor, fixated on existential questions of human suffering and purpose. His sole acknowledged pleasure was consuming mapo tofu, its intense spiciness briefly alleviating his emotional void. Philosophically, he viewed himself as a contradiction: inherently evil yet not inhuman, asserting that humans who know evil but choose good are superior to angels ignorant of darkness.