User blog:WanderingAsura/Sword of Exorcism

The Sword of Exorcism is the main weapon of the Medicine Seller, used by his other self to slay mononoke. However, this demonic-looking sword is enchanted so that in order to unsheathe it, the Medicine Seller must find the Katachi, Makoto , and Kotowari of a particular mononoke he wishes to exorcise. The sword is usually silent. However, once all three secrets have been gathered, the sword yells "Tokihanatsu". Once the sword has been unsheathed, he transforms into a mystical and powerful being that is more or less an inverted version of himself. The blade itself is composed of ethereal energy that can cut and seal any mononoke, and can expand in size in order to take out larger threats.

The common theory as to the sword needing the Three Secrets is that either the sword, the Medicine Seller or both need to empathize with the mononoke before slaying it. Whether or not this is the case (and if so, why) is never explained.