Caster must be defeated. Different from Kiritsugu, Saber had her reasons to defeat Caster by her own hand. She must subdue that devil even if she suffers heavy wounds and damages her strength. This is the duty of the King of Knights, an inescapable obligation. A devil that sullied the meaning of war, a scum that humiliated the pride of humans; Saber would never let such a person go.

- Fate/Zero: Act 6, Part 2