Light's Blessing is an item exclusive to Fire Emblem Heroes.
Light's Blessing is a consumable item that allows a player to fully revive all allies on a current map, restore all ally units to full HP, rejuvenate all allies to move again if they have already, and all Special skill cooldowns are instantly fully charged.
Players can consume a Light's Blessing at any time during a battle except in Arena battles. If all ally units are downed on a map, players are given the option to use it on the Game Over screen. If the player does not have a Light's Blessing, they can also consume an Orb for the same full effects as a Light's Blessing.