The Clef Blade is the traditional weapon of choice of the Coda Sisterhood. It is more of a ceremonial weapon than one of practicality, and it only intended for use in Coda duels and rituals. Some Coda however, such as Devin, have used the Clef Blades in order to become dangerous assassins.
The Clef Blade seems to emit a type of vorpal energy field while in use, one that further sharpens its already deadly edge.
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