Pierce Resist

Pierce Resist is a effect in Xenoblade Chronicles and Future Connected. It adds a percentage chance that the user will not be affected by the debuff.

Overview
Pierce is most detrimental to armour tanks, so a gem that protects against it is probably best-served on them. Characters without much defence still don't like being pierced, and it can be worthwhile to give them some protection against it so they don't take even more, but on an expected-value basis it's better to put it where the most damage is going and the most defence would be affected.