Rule Breaker

is a weapon that materializes and embodies the Divinity of the Witch of Betrayal. It is an iridescent and jagged dagger that is thin, brittle, and blunt. Its effectively nonexistent in its capacity as a weapon, comparable to that of a regular dagger at most, and it would not be suitable for even killing a single person. Caster is able to use it against normal humans, slaying her original Master and cleanly cutting off Shirou's arm without issue. Shown by the complex shape of the blade, 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 has forgiven anything for one purpose." Such ceremonial knives are designed as mere decoration, and like those, Rule Breaker was created under the school of thought that it was never to be used as a weapon. 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.
Greatly differing from other Noble Phantasms, the conceptual ritual tool's unique ability is that it is the ultimate anti-magic Noble Phantasm capable of dispelling and destroying any kind of magecraft, an effect suitable to the Noble Phantasm that is a manifestation of Caster's nature as the "Witch of Betrayal". A dagger that nullifies all effects created by magecraft, despite whether such an effect is an enchantment, a relationship formed through contact, or even life created through magical energy. Once it comes into contact with the ensorcelled item or person, enchantments, connections bounded through contracts, and creatures created and maintained by magical energy, they will all be returned to their original components in a state "before they were made." Contracts will be wiped clean and those with life will immediately cease to exist. There is a limit to what it is able to dispel, artifacts on the rank of Noble Phantasms will never be returned to their original state no matter how low their rank. It may be able to dispel and break any and all forms of Magecraft, and may even work on Servants and nullify their contracts, but it is impossible for it to work on other Noble Phantasms, especially ones designed to ward off attacks and thus are difficult to even penetrate.Fate/Grand Order - Thomas Edison Interlude I: Can You do It?
rulebreaker.jpg|Caster nullifying the contract between Saber and Shirou.
Caster using Rule Breaker on herself.gif|Caster using Rule Breaker on herself to break her hold on True Assassin.
Shirou using Rule Breaker on Sakura.gif|Shirou using Rule Breaker to nullify Avenger's contract with Sakura.
Miyuverse Sakura using Rule Breaker to break Miyuverse Shirou's contract with Archer.jpg|Sakura using Rule Breaker to break Archer's Class Card Contract with Shirou.
Shadow Medea using Rule breaker on Ritsuka.png|Shadow Medea using Rule Breaker to free Ritsuka from Abigail.
 
While its uses are limited under normal means, it has high effectiveness in the Holy Grail War due to being able to manipulate the Servant System. 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. She can also turn the dagger on herself, severing her contract with her Master without establishing a new one in its place. This does not seem to do anything to the Command Spells as Atrum Galliasta did not lose his after Caster severed their contract this way; however, without a contract, they become vestigial and useless in Galliasta's attempts to force Caster to commit suicide.Fate/stay night [Unlimited Bladeworks] - Episode 14: "Princess of Colchis" The Servants themselves must be the target as it has no effect on Shirou's contract with Saber from simply stabbing his flesh. It is also capable of severing Angra Mainyu's hold on Sakura Matou after it is projected by Shirou. It even has the ability to sever Class Card contracts, as shown when the Sakura of Miyu's world uses it to save Miyu's Shirou from his overuse of EMIYA's powers.Fate/kaleid liner PRISMA☆ILLYA 3rei!! - Chapter 73.1: "Shoot"
==References==
vi:
Category:Noble Phantasms
Category:Anti-Thaumaturgy Noble Phantasm
Category:C rank Noble Phantasms
Category:C+ rank Noble Phantasms
Category:Knives
Category:Mystic Codes
Category:Noble Phantasms introduced in Fate/stay night
Category:Noble Phantasms in Unlimited Blade Works
Category:Noble Phantasms of the Argonauts