Rule Breaker

Lore & Background

In the Heaven's Feel route of Fate/stay night, Rule Breaker is used by Caster, the Servant of the Master Sōichirō Kuzuki. The weapon's primary function is to nullify and destroy any form of magecraft, including the sacred contract between a Master and Servant. This makes it a devastating tool in the Holy Grail War, as it can instantly turn a powerful Servant into a free agent or leave them stranded without a prana supply. The dagger itself is not a weapon of direct combat but a ritual implement of immense magical potency. Its existence is a direct threat to the very foundation of the war, as it can undo the summoning process itself.

Reader's Guide

Rule Breaker is a Noble Phantasm of Caster (Medea), classified as an Anti-Magecraft weapon. Its effect is to nullify any magical contract or enchantment upon contact. In the context of the Holy Grail War, this means it can sever the bond between a Master and Servant, effectively freeing the Servant from their Master's control. The dagger must make physical contact with the target to activate its effect. It does not cause physical damage but instead disrupts the magical energy binding the contract. This makes it a highly situational but potentially war-winning tool, as it can turn an enemy's Servant into a neutral party or even an ally. However, its use requires precise timing and close-quarters access to the target, making it risky in combat. In the Heaven's Feel route, Shirō obtains the dagger from Caster's remains after her death and uses it to save Sakura.

Did You Know?

• Rule Breaker is the Noble Phantasm of Caster, whose true identity is Medea from Greek mythology.
• In the Heaven's Feel route, Shirō Emiya uses Rule Breaker to sever Sakura Matou's connection to the corrupted Holy Grail.
• The dagger's effect is not limited to Master-Servant bonds; it can break any form of magecraft, including enchantments and curses.
• The weapon's name in Japanese is "Rule Breaker: Subete no Mahō o Kudaku Mono" (All Spells Must Be Broken).