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Class cards are Manifestations of heroic spirits summoned during each Holy Grail War, corresponding to one of Several classes. The cards have a portion of the Heroic Spirits' power sealed inside them, and it can be said that they are the Heroic Spirits themselves. They draw out the power of Heroic Spirits, allowing either a Mystic Code or the user's own body to act as a medium for the Heroic Spirit's power. Overwritten by a fraction of the Heroic Spirit's power, they are able to fight others with that power.
The Rule Master of the Ainsworth Holy Grail War is the only individual with the authority to create or destroy Class Cards.
Include Temporarily materializes the weapon or Noble Phantasm of the hero by overwriting a Mystic Code. Users can Include a card even while having a card Installed. The command to end the Include is Uninclude But is weaker Then becoming the spirit itself with install but makes up for it in versatility Like having Sigfried's sword and Achilles shield at the same time but doing so locks out any special advantages these servants had like Siegfried's invulnerability .
Unique to the Berserker Class Cards, Installing Berserker and then Installing another card confers the properties of Berserker to that Card's Heroic Spirit given gates increased damage and strength that can ignore the wounds at the cost of rational thinking.