Fate/Zero: Why Kirei vs Kiritsugu Is A Brilliant Fight

gamerant.com:

Gen Urobuchi's Fate/Zero is regarded as one of the high marks of the Fate mythos and the perfect prequel to the already acclaimed Fate/Stay Night, but its battles were something special. In what is often called an anime Game of Thrones, the story's Holy Grail War was relentless, smart, and dripping with philosophical and interpersonal drama.

Over 24 episodes, the players all battled one another, taking pieces off of the board one by one and revealing more and more of their dark side in the process. In the final episodes, it came down to two major parties: the agent of the Holy Church, Kirei Kotomine, and the Mage Hunter and aspiring Hero of Justice, Kiritsugu Emiya.

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While there are a few key characters that can be considered the main characters of Zero, Kiritsugu Emiya may be the single most central character in the grand scheme of things. He's an uncharacteristic participant in the Holy Grail War, having courted favor with the Einzbern clan to be sponsored as a master, despite a storied career as a hunter of mages. His attitude, his ethic, and his strategies are all more comparable to a world-class assassin rather than any typical master if masters can even be typical. Using his intelligence and his reconnaissance of other masters and servants, he adeptly avoided getting picked off throughout the war and found himself at the end, though not without playing some dirty tricks.

Kiritsugu is someone that will perform any manner of cruelty to win the war so that he can end suffering on Earth, believing that the ends have to justify the means. The promise of the Holy grail makes his fighting worth the blood on his hands, so long as he can make a better world for his daughter;