Slot Reels are Wakka’s Overdrive and other than the first one, the rest are unlocked via Blitzball. You will need to finish at least 450 battles in the main game, outside of the Monster Arena, in order to make the last one available. Attack Reels is won from a tournament, Status Reels from a League (following Attack Reels), and Auroch Reels from a Tournament (after obtaining Status Reels).