Kiritsugu Emiya: His Own Worst EnemyKiritsugu was shown to be akin to Fate/stay Night's Shiro Emiya in his youth, a Wide-Eyed Idealist who sought to be a "hero", but his experiences moulded him into a Well-Intentioned Extremist, noted for coldness and extreme measures, which he justified to himself by substantiating The Needs of the Many, a belief that was instilled in him by his own past, and the realisation that not everyone could be saved. His pragmatism extended to the point of standardising the value of lives to justify the murder of innocents, establishing him as a Byronic Hero, and serving as the chief source of friction with his honor-driven Servant.
When he entered the Fourth Fuyuki Holy Grail War as the Einzbern's representative, Kiritsugu had already become a husband and father. This transition from a child mercenary fighting for his own sense of justice shows a brief lapse in his bloody pursuit for peace, but it was not for domestic happiness that he briefly settled down. His introduction to the Einzberns and the Holy Grail gave him new hope in his childlike belief that everyone could be saved, so he would commit to the notion of winning the Grail War. Ironically, he would use his adult tactics and pragmatic schemes to try and win the War itself.
- Kiritsugu: I'll ensure that the blood I spill in Fuyuki is the last that humanity will ever shed.
In his own words, Kiritsugu hoped to end the violence with the Holy Grail War, and took Necessarily Evil steps to that end, as he always had. However, as the war comes to an end, he is struck by the revelation that the Holy Grail can only satisfy wishes through means known to the wisher. In Kiritsugu's case, this means killing the few to save the many, only the Grail twists this to interpret it as genocide.
Kiritsugu is viewed as an Anti-Hero for his deeds, but is just as qualified as a Tragic Hero due to the progressive destruction of his ideals and beliefs. Genocide aside, Kiritsugu fundamentally couldn't accept a utopia created by violence: it was to avoid this, the ugliness of his own methods, that he sought omnipotence. Discovering that even the Grail couldn't solve his vicious cycle of violence may well have been his Despair Event Horizon. Even so, he chose to continue as the Knight Templar by trying to destroy the Grail, but even this would backfire, killing hundreds of innocents and achieving nothing.
This would serve as his Moral Event Horizon, finally breaking him. Having committed everything to a single glimmer of hope, only for his very identity to thwart his chance destroys his very belief that he can bring about positive change in the world. That being done, he desperately searches for survivors: his first and last straightforward act of "heroism", one that reflected his youthful desire to help people, ironically done out of racking guilt and in search of redemption. This would be Kiritsugu's last deed as a man seeking to be a hero, and his first true act of heroism.
His ideals destroyed and his life ebbing away from the aftermath, Kiritsugu would find solace in the fact that he saved a single child, Shiro, who would inherit Kiritsugu's ideals with the same childlike optimism that Kiritsugu based them on. Finding peace in the knowledge that his ideals may yet survive in the world without his self-damning methods, Kiritsugu entrusts them to his adoptive son before passing on.