Despite his duty, Assassin allows Saber to escape with a wounded Shirou because he is moved by her compassion and desires a more "honorable" future duel. Character & Lore Developments
The seventh episode of , titled "A Reward for the Struggle," is a critical turning point that shifts the focus from external battles to internal ideological conflicts between Shirou Emiya and Archer. Core Conflict: Ideological Clash
Realizing his current weakness after the encounter with Archer, Shirou finally asks Saber to train him in swordsmanship so he can defend his own ideals. Fate Stay Night Episode 7
Fate/stay night [Unlimited Blade Works] Episode 7 Discussion
He argues that "saving everyone" is an impossible dream. He intentionally lets Caster go, believing she will grow strong enough to defeat the greater threat, Berserker, even if it costs innocent lives in the process. Despite his duty, Assassin allows Saber to escape
He believes a hero must save everyone and refuses to align with Caster because she uses innocent people as mana sources.
This disagreement leads Archer to literally stab Shirou in the back, attempting to kill him to eliminate what he views as a dangerous, naive ideology. Key Servant Encounters Fate/stay night [Unlimited Blade Works] Episode 7 Discussion
It is revealed that Caster has broken the standard rules of the Holy Grail War by summoning her own Servant, Assassin , to guard the Ryuudou Temple.