Summon Aqua is one of Melia's EtherArts in Xenoblade Chronicles. It is a support art that restores Melia's and nearby allies' HP every 3 seconds while the elements is active. Melia can sacrifice this buff with Elemental Discharge in order to absorb some of the target's HP.
Advanced art books are only available from enemy drops. For any enemies listed with a 0% drop rate, the item can only be obtained using Yoink!, Riki's Talent art.