There are a handful of aeons you can get on your journey. The vary in the power, skills and personalities. Some even you require payment.
The first aeon you will receive is Valefor
Valefor
Received in Besaid
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Elemental:No
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Special Attack:Sonic Wings-Deals damage and delays enemies turn.
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Overdrives:Energy Ray-Valefor shoots a ray of energy across all enemies dealing damage.
*Secret Overdrive*-Energy Blast-Makes a glpyh and shoots multiple energy blasts at all enemies dealing damage to all enemies. To get this overdrive go to Besaid village. On ther first shop to the left buy some potions. Then attempt to talk to the dog. Leave and enter the temple. Come back to the store. There should be a girl by the dog now. There may be no one there. If so, leave and come back.Talk to the girl by the dog. Congratulations!
Ifrit
Received in Kilika
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Elemental:Yes (fire)
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Special Attack: Meteor Strike-Deal damage to an enemy.
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Overdrive-Hellfire-Deals damage to all enemies.
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Ixion
Received in Djose Temple
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Elemental:Yes(Thunder)
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Special Attack:Aerospark-Deals damage and negates all spell affects.
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Overdrive-Thors Hammer-Deals damage to all enemies
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Shiva
Recieved in Macalania
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Special Attack:Heavenly Strike-Deals damage to enemy, delays turn.
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Overdrive:Diamond Dust-Deals damage to all enemies.
Bahamut
Received in Bevelle
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Elemental:No
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Special Attack:Impulse-Attacks all enemies
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Overdrive:Mega Flare-Deals damage to all enemies.
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Yojimbo
Received in Chamber of the stolen Fayth
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Elemental:No
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Special Attacks:Daigoro-Attacks with dog dealing damage to one enemy.
Kozuka-Pulls three blades and throws them at an enemy dealing damage.
Wakizashi-Deals damage to one enemy but sometimes may deal damage to all enemies.
Zanmato-Instant death to ANYTHING (I mean anything!)
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Overdrive:Yojimbo has no overdrive but is more likely to do Zanmato with a full gauge.
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Yojimbo requires payment for his attacks.
Anima
Recieved in Baaj Temple.
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Elemental:No
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Special Attack:Pain-Deals damage to one enemy and inflicts death.
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Overdrive:Oblivion-Deal damage to all enemies.
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Magus Sisters
Recieved in Remiem Temple
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Cindy
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Elemental:No
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Special Attack:Camisade-Deals damage to one enemy.
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Overdrive:Delta Attack-Deals damage to all enemies.
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Sandy
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Special Attack:Razzia-Deals damage to one enemy.
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Overdrive:Delta Attack-Deals damage to all enemies.
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Mindy
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Special Attack-Passado-Repeatedly Attacks one enemy.
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Overdrive:Delta Attack-Deals damage to all enemies.
Here you go Lisa!