Earth Rave is obtained by using Howling Moon six times. Red XIII can equip the Cover Materia to speed this up, and using a Hyper on him gives the Fury status that doubles the rate Limit gauge fills. For specific grinding, a good location is the large forest in the Nibel Area past Mt. Nibel where enemies appear in large groups (helping other party members acquire Limit levels that require multiple enemy kills), and have attacks that deal enough damage to raise Red XIII's Limit gauge considerably. One enemy fought here, Valron, uses Gravity-based attacks that reliably increase Red XIII's gauge quickly with no risk of killing him.
Earth Rave deals five hits that are randomly distributed among enemies. Each hit deals 1.825 times Red XIII's normal damage, totaling a damage output of 9.125 times his base damage. As it is based on his physical damage, it relies on his weapon and Strength stat. Earth Rave has the highest single-target damage output of any of Red XIII's Limits, as his ultimate Limit Break, Cosmo Memory, hits all enemies only a single time.
Though Cosmo Memory is initially a better Limit Break for Red XIII, and is throughout most of the game, if he equips Limited Moon and reaches a high enough Strength stat through Power Sources, Earth Rave can easily deal five hits of 9999 damage. Though Stardust Ray hits for ten times, Earth Rave has an easier time of reaching maximum damage due to the high potency on each attack.