Luna (月光 Gekkou, lit. Moonlight), also known as Moonlight Sword (月光剣, Gekkouken, Lunaire in the French version) and Pierce, is a skill that is first introduced in Fire Emblem: Genealogy of the Holy War. When activated, this skill allows its user to negate or halve the enemy's Defense, allowing him/her to inflict higher amounts of damage in the process.
The Pierce skill in The Sacred Stones is associated with a game-freezing glitch, which generally happens by activating Pierce on an enemy when the attacking unit will attack twice in a row, on an enemy that cannot counter-attack, which can also happen with a Brave Lance. If the enemy is not killed on the first strike and attacks a second time, a freeze may occur. The root of the glitch seems to be dealing damage again to an enemy before their HP bar has finished decreasing. This glitch does not occur in the Japanese version of Sacred Stones. This glitch does not seem to happen if animations are turned off.