The Aster Protoflorian is a reasonably tough boss, but Lightning and Hope don't really have that many options open to them, so it is simple by necessity. Protect and Shell will help, and should be kept up throughout. Unless someone needs healing, you'll generally want to rotate between Slash & Burn and Dualcasting to stagger the boss quickly, then Launch it. If things go really badly, don't hesitate to SummonOdin to finish the beast. Even if it doesn't finish it, summoning restores your party to full health.