During the time where the player has to protect Queen Minnie from the Heartless that have infested Disney Castle, more specifically, the Throne Room, the player will have access to use Faith. The Reaction Command appears if you stay with Minnie for a little while. It is especially effective as one or two blasts can destroy large numbers of Heartless, and, although it appears to be a spell, it consumes no MP. It is presumably of the light attribute, though this is not made especially clear.
Faith takes the form of a large blast of pink and white light, and is able to vanquish all Heartless in the immediate area, though it does not prevent more from spawning. Sora jumps in the air, raises his Keyblade, and says "Let's go!". Minnie ascends a few feet and a column of swirling white light appears around her, she then says "Light!". There is a huge white explosion and a white shock wave is sent out from the base of the column.