Nailsmith

Found in the City of Tears at the far left of the map from the bottom. The Nailsmith is indicated by a nail sign pointing to his house near the elevator at the entrance of the City.

Nail Refinement
He'll provide the first nail refinement for Geo, after which he'll require Pale Ore and Geo to upgrade further.
 * First Upgrade: 250 Geo
 * Second Upgrade: 1 Pale Ore and 800 Geo
 * Third Upgrade: 2 Pale Ore and 2000 Geo
 * Fourth Upgrade: 3 Pale Ore and 4000 Geo

*MAJOR SPOILERS* After fully upgrading your nail, he wants to feel the bite of his greatest work.