It can be purchased once from the Bazaar by selling Bat Wing x1, Grimoire Aidhead x3, and Grimoire Togail x3. It can also be acquired from treasures in Mt Bur-Omisace, Archades and Cerobi Steppe with the Diamond Armlet equipped. All of these chests respawn but the chance of acquiring Dark Energy from them is low due to the chests spawning rarely and the chance of acquiring gil rather than the Dark Energy being 80%. Using Dark Energy does not require charging. Dark Energy deals 50,000 damage to all visible foes and uses the same animation as a Megalixir.