Crystals scattered in the various battle arenas protrude from the ground, and standing next to them will replenish your character's magic. The crystals vary in color, correlating to the four elements--they'll replenish anyone's magic, but characters with a matching element will replenish faster. Here's a tip: stand next to a magic replenishing crystal and you can continue to use your magic--either for attacks or defensive strategies--while your magic builds back up. Your magic won't run out until the power in the crystal is exhausted.