Ifrit
Ifrit is the second Aeon that Yuna receives and is a reoccurring summon in the Final Fantasy series. She receives it after you complete the Kilika Cloister of Trials. Ifrit can do regular attacks as well as an attack called Meteor Strike.
Overdrive: Hellfire
Note: Both Meteor Strike and Hellfire are fire-based attacks. Make sure that the enemy you are facing is not either resistant, immune or able to absorb fire magic.
Ifrit will be able to break the 9,999 damage limit after you have obtained World Champion and upgraded it using the Jupiter Crest.