Final Fantasy X: Yuna Overdrive - Grand Summon

Yuna‘s Overdrive is Grand Summon, and it is the only Overdrive she gets in the game. When executed, she will summon an Aeon of your choice with a full Overdrive bar. Something to note is that if you use Grand Summon to call an Aeon whose Overdrive bar is already full, it will have two full bars, allowing you to use their strongest attack twice. You do not have to do anything to obtain Yuna’s or her Aeon’s Overdrives besides recruiting the Aeon, with one exception (see Valefor’s Hidden Overdrive below).

Aeon Overdrives

Aeon	Overdrive	Effect
Valefor	Energy Ray	Deals non-elemental damage to all enemies.
Valefor	Energy Blast	Deals non elemental damage to all enemies (stronger than Energy Ray).
Ifrit	Hellfire	Deals Fire damage to all enemies.
Ixion	Thor’s Hammer	Deals Lightning damage to all enemies.
Shiva	Diamond Dust	Deals Ice damage to all enemies.
Bahamut	Megaflare	Deals non-elemental damage to all enemies.
Anima	Oblivion	Deals sixteen non-elemental attacks to all enemies.
Magus Sisters	Delta Attack	Deals six non-elemental attacks to all enemies. All three sisters must have a full Overdrive bar to execute.

Yojimbo is the only Aeon without an Overdrive. However, a full Overdrive bar increases his chance of using better attacks such as Zanmato.

Valefor’s Hidden Overdrive

Valefor is the only Aeon who can get two Overdrives, and her second one is hidden in Besaid. To obtain it, you must talk to the girl in the shop. Then go the third tent on the right. Inside talk to the dog, and Valefor will learn Energy Blast. You can get this at any point in the game where you have access to Besaid, but note that if you wait until you get the airship, you will have to fight a superboss before you can learn it.