Awakening & Fates
Its activation rate is based on skill. It halves damage from Bows, Tomes, and Dragonstones. It does not activate Dual Strikes. In Fates, this was fixed.
The Heroes version is simplified to just attacks inflicted from 2 spaces away and reduces damage by 50%. It has a 3 turn cooldown and costs 200 SP. It requires that the character is a Melee character and the character learn Holy Vestments first.
Aegis is a Lunatic+ mode enemy-exclusive ability with the same effect except that always activates.
In both Awakening and Fates, the skill is learned by Paladins at level 15.
In Heroes, it is learned by the following characters without skill inheritance at the rarity levels listed