Nagi Nagi no Mi

The Nagi Nagi no Mi is a Paramecia-class Devil Fruit that allows the user to become a "Soundless Human". Nagi (凪) means "null" in Japanese. It was eaten by Rocinante, but with his death the fruit has returned to circulation.

Strengths and Weaknesses
The user of this Devil Fruit has the ability to create a soundproof field. The field makes that the sounds from the outside cannot be perceived from the inside. This applies in reverse too, making the sounds inside the field unperceivable from the outside.

This fruit seems to have no offensive capabilities. Other than that, it has standard Devil Fruit weaknesses.

Usage
Rocinante uses this fruit rarely as to conceal it from his crew, and uses it in order to have a private conversation with Trafalgar Law.