Shields can be upgraded from the second playthrough onwards after defeating the final boss. They can be upgraded at forges for a small fee and various materials that can be bought at the Adventuring Essentials, or obtained from defeated enemies. The best materials are only available as enemy drops. One can also downgrade shields, but this will not refund the materials used to upgrade them although it does "refund" the number of upgrades. Downgrading can therefore be considered as the backup plan in case one upgrades a shield the wrong way.