A Soul Catalyst is a special item designs to allow for easier use of Soulcraft.
Soul Catalysts are special items that allow a user to perform Soulcrafts easier by channeling their Anima through the item instead of directly outwards, which allows for easier Anima control as well as more powerful Soulcrafts depending on the specific Soul Catalyst used. Soul Catalysts react with the ambient Anima of Creation in order to fuel their power, and the user of a Soul Catalyst is then able to infuse the item with their own power to perform a Soulcraft.
Soul Catalysts are different from normal weapons under the effects of Anima Infusion in that Soul Catalysts are designed to have Anima flow through them instead of just around them.
From a technical standpoint, soul catalysts are rated by resistance grade. The resistance grade is a measure of the amount of resistance an object produces against Anima flowing through it. Objects with high resistance are much more resistant to the Anima being put through them, requiring more power in order to get Anima to run through. Anima resistant material, therefore, makes excellent protection against Anima-based attacks and weapons, though a completely 100% resistant material does not exist naturally or artificially. Objects with less resistance, by contrast, offer less resistance to Anima being put through them, and this is the main goal of soul catalysts. The less effort required to put energy through the weapon, the stronger the weapon can be. The extinct Rythulian race were able to achieve weapons with incredibly low resistance, very near perfect zero, resulting in very powerful weapons, the power of which still has not been matched. The only weapons known to be even more powerful, achieving perfect zero resistance, are the Soulblades.