When cast, a series of rainbows manifest and charge at the entire wave of foes, striking them repeatedly for weapon-elemental damage. While Rainbow Blast doesn't have a cooldown like most multi-target weapon-elemental skills (Arrow Rain, Slicing Cyclone and Swift Slash), it also halves the status chance of Natalie's staff, making it significantly less useful for spreading status effects/debuffs.
Epic Battle Fantasy 5
Rainbow Blast is the upgraded version of Spectrum. It can either target all foes or just one, acting like Spectrum when used against a single target.