Rule Breaker

Rule Breaker: All Spells Must Be Broken (破戒すべき全ての符(ルールブレイカー)) is a weapon that materializes the divinity of the witch of betrayal. It is a iridescent and jagged dagger that is thin, brittle, and blunt. It has the combat efficiency of a regular dagger, and it would not be suitable for even killing a single person. Its actual purpose is that of a key used for rituals that is described by Caster as an "indulgence from the Age of Gods that is forgiven anything for one purpose." Shirou feels an ominous feeling every time he encounters it, realizing it is dangerous to Servants after inadvertently analyzing it, manifesting as a feeling of pain in the Command Spells on his hand.

Its unique ability is that it is the ultimate anti-magic Noble Phantasm capable of dispelling and destroying any kind of thaumaturgy. Once it comes into contact with the ensorcelled item or person, enchantments, connections bounded through contracts, and creatures created and maintained by prana will all be returned to their original components in a state "before they were made." It is a blade of betrayal that will sever all connections between a Master and Servant by destroying every single rule that controls them, giving full control of the Master's Command Spells to Caster. She uses this on both Saber and Archer, causing Shirou and Rin's Command Spells to instantly disappear and transfer to Caster after their contracts are nullified. It is also capable of severing Angra Mainyu's hold on Matou Sakura after it is projected by Shirou. It has no effect on Shirou's contract with Saber from simply stabbing his flesh, and it would be impossible to return another Noble Phantasm to its original state.