He was the victor of the 4th Holy Grail War. When it ended he adopted Shirou from wreckage of the war.
Emiya Kiritsugu is the father of Illyasviel von Einzbern and Emiya Shirou. He has a minor role in Fate/stay night and is is one of the major characters is the novel prequel Fate/Zero. He was a freelancer and infamously known as the Magus Killer.
Born on an Arimago Island, Kiritsugu lived with his father Emiya Norikata, fourth family head of the Emiya family and a magus who received a Sealing Designation. He became friends with - and had a crush on - Norikata's assistant, a local girl called Shirley who was four years older than him. However, disaster struck when Shirley somehow became a vampire and pled for Kiritsugu to kill her. Their village is overrun by Executors from the Church and Enforcers from the Association, both groups having arrived when they heard rumors of a magus researching into vampirism. Kiritsugu was the only survivor of the 'cleansing', saved by Natalia Kaminsky, a freelancer and part-time Enforcer who wanted information on the magus responsible.
Returning to the hidden Emiya residence, Kiritsugu confronted his father on his research and Shirley's death. Noritaka explained that he wanted to become a Dead Apostle to continue his with his research on Magecraft longer. Shirley apparently drank one of his potions out of curiosity. Just as Norikata was planning their escape, Kiritsugu shot him in the back with a pistol - Natalia figured that the only person who could prevent Norikata from escaping and ensure his death was his own son. In the end, Natalia took Kiritsugu with her.
Realizing that the tragedies he saw in his childhood were common occurrences in the world, the teenage Kiritsugu became a freelancer like Natalia to hunt down heretical magi around the world. Natalia trained him not only in Magecraft, but in tracking, assassination, and all types of weaponry.
During one mission, they were following a Dead Apostle who was on an Airbus A300 jumbo jet; Natalia was in the plane during the flight while Kiritsugu waited at the destination. As every single passenger had become undead, Kiritsugu deemed the situation too risky and shot the plane down before it could land, sacrificing Natalia in the process. In their last conversation via radio, he admitted that she was like a mother to him. It was then that he became disillusioned with his ideal of becoming a 'hero of justice', as it was impossible to save one person without losing another. However, he continued to fight for this dream, to ensure that everything he had given up would not be in vain.
He was eventually branded as a Magus Killer by the Association, though the higher-ups often found uses for a hitman and treated him much like the Church treats its Executors. To the Church itself, he is considered 'an individual that requires surveillance'.
Around eleven years before the fourth Holy Grail War, he took on a younger soldier as his apprentice, who he eventually named Hisau Maiya, training her in much the same way Natalia trained him. She became his assistant in the field and also his 'lover', in a purely sexual context.
Emiya Kiritsugu is created by Gen Urobuchi and designed by Takashi Takeuchi as one of the main characters for the Fate Zero anime series. Kiritsugu has no information regarding any inspirations used to create him. He originally appears in the visual Fate Zero, and makes his first anime debut in Fate Zero episode 1, Summoning the Ancient Heroes. He is voiced by Rikiya Koyama in the Japanese version.
Two years later, Kiritsugu was hired by the Einzbern family to be their representative in the coming conflict. Believing that the Holy Grail could grant his wish for world peace, he left behind his work as a 'hero of justice'. Using his sperm, Irisviel von Einzbern artificially conceived a child, named Ilyasviel, who was born one year later.
Despite being the true Master of the Einzbern, Kiritsugu operated mostly in the background during the conflict, ambushing other Masters when they were otherwise occupied, while Saber, who was summoned using Excalibur's lost sheath as a catalyst, was partnered with Irisviel and made to act out in the open. This was to avoid conflict between Kiritsugu and Saber, as the methodologies of the two conflicted with each other too much. Saber and Irisviel traveled from Einzbern's castle in northern Europe to Japan by plane, while Kiritsugu took a different route, entering Fuyuki by ship and meeting with Maiya.
In the climax of the war, Kiritsugu fought the last Master, Kirei Kotomine to a standstill, both being consumed by the black 'mud' flowing out from the Holy Grail. There, Kiritsugu met 'Irisviel' again, now completely merged with the Grail. In his mind, he was forced to confront the fact that his methods will eventually lead to him becoming the ultimate enemy of humanity, equal to Angra Mainyu itself - and, 'Irisviel' proclaimed, this path is correct. Kiritsugu, now realizing that the Grail is corrupted, rejected 'Irisiviel', who placed a curse on him - to never be free of regret until his painful death. Kirei, having went through the same experience, asked Kiritsugu why he rejected the Grail; Kiritsugu killed him after a vague response.
Kiritsugu appeared during the final battle between Archer and Saber and used all his remaining command spells to force Saber to destroy the Grail with Excalibur, causing her to fade away. However, Kiritsugu realized immediately after that this was a mistake - without a vessel to contain it, the 'mud' spilled from its core onto the streets below, causing a fire that eventually destroyed a large part of Shinto.
With the war's end, Kiritsugu discarded his merciless facade and sought to atone for his gruesome deeds. When he stumbled upon a dying Shirou, seemingly the only survivor after the fire, he was overjoyed at the opportunity to save a life. In order to revive him, Kiritsugu implanted Avalon into Shirou's body. Kiritsugu later adopted him as a son, settling in the new Emiya residence that he bought during the war.
He met Taiga Fujimura sometime after, and took a liking to her due to her similarity to Shirley. Once Shirou was old enough, Kiritsugu left Fuyuki several times, traveling back to the old von Einzbern castle, trying to save his daughter. However, he never managed to find his way past the bounded fields, having lost most of his magecraft abilities.
To ensure the destruction of the Great Grail, Kiritsugu used explosives to create a 'bump' in the nearby leyline, which would ensure a earthquake in thirty to forty years' time. By doing so he hoped to prevent a fifth war, but did not realize that the incomplete ending of the fourth war would cause the next war to occur in just ten years.
Angra Mainyu's curse eventually cost his life, as his limbs were lame, his sight failed, and most of his circuits became useless. He died at the age of thirty-four, five years after the end of the War, passing onto Shirou his ideal of a 'hero of justice'. He is buried in the graveyard behind Ryuudouji, though Shirou rarely visits.
Kiritsugu is only average as a magus. However, he is unusually skilled in penetrating bounded fields, breaking through the field around the Tohsaka residence in about three hours when it would have took a normal magus a year. He also deliberately uses what would be unconventional methods to magi. He possessed dual Elements of Fire and Earth, which is linked to his dual Origins, Severing and Binding.
As the Association had retained Norikata's corpse under the Sealing Designation, Kiritsugu only inherited a fragment of the Emiya Thaumaturgical Crest, less than 20% - "the dregs". However, the magi of the Emiya bloodline focused on 'time manipulation', and Kiritsugu had little interest beyond what could be applied for combat use. This culminated in his unique style of magecraft.
Like the ability of the fifth War's Archer, this is an imitation of magic: a bounded field close to a Reality Marble that is physically limited to Kiritsugu himself, allowing him to regulate time within the field - that is, speeding up (accel) or slowing down (stagnate) his own body. As it is deployed in its smallest scale, it can adjust time by a few seconds at most.
However, there will be inconsistencies between the flow of time inside and outside the field; as soon as the field is removed, natural forces, the world itself, will forcefully adjust the 'incorrect time'. This damages Kiritsugu physically every time Innate Time Control is used, to the point of crushing his bones. Due to this, he apparently never went beyond double accel, though he effected triple and quadruple accel in his battle against Kirei as he had Avalon's potent regenerative abilities at the time.
As a spellcaster, Kiritsugu treats magecraft as a tool and supplements it with technology to gain an advantage. In addition to his preference for firearms, he also uses explosives - grenades, plastic explosives, and landmines.
A submachine gun used as sidearms by Kiritsugu and Maiya. Compact model is equipped with a sound suppressor, laser sight, and foregrip.
Thompson/Center Arms Contender
The symbol of Kiritsugu as a magus: his Mystic Code, a customized pistol with a grip and forearm carved in walnut, reminiscent of a dagger in its scabbard. It is a conceptual weapon designed to fire Kiritsugu's special 'magic bullets'.
Kiritsugu's sniper rifle, fitted with both an AN/PVS-4 night scope, and an offset Specter IR thermal scope. The thermal scope is used primarily for infrared imaging, as Kiritsugu could read the status of a magus' Magic Circuits through their thermal signature.