Mythril

Mythril...is a rare type of metal that shines with silver light. It has the power to banish the darkness that dwells within demons. Mythril (ミスリル Misuriru) is a rare type of metal that can nullify the abilities of Devil Fruits. It is often forged into equipment as a countermeasure against Devil Fruit users, especially the Logia-class.

Trivia

 * Mythril is a reference to Mithril in J. R. R. Tolkein's writings such as The Hobbit and The Lord of the Rings.