Diamond

 is a raw material used for revising weapons at the Forge.

Obtaining
can be rarely obtained from quarrying rocks and gathering Animal Feces.

Two s are also dropped by the Rock-on boss that can be found on the Upper Level of the Ingall's Mine, in the mission, and on various levels in the Deepest Ruin.

Usage
s are required to update certain types of swords to new attributes at the Forge.

Gift
can be given as a gift to other characters.