fight seymour normally at first because the first stage of this battle is easy. then summon the new aeon labelled ???? in the summoning list. you will summon the ice aeon shiva. fight anima and use heavenly strike or normal attack and wait until animas attacks fill the overdrive gauge.it should take 2 or 3 overdrives to beat anima. use blizzara to heal shiva when shes on low HP. now its the hard part. with anima defeated its seymour. he only has 6,000HP but is very powerful. have a weapon with the sensor ability to see the pattern of spells he uses. he always uses spells in a certain order so if you use nul spells at the right time it will make his magic do no damage and make him weak and useless. dont summon your aeons against him unless they have full overdrive because they wont last 2 seconds against seymour.

as for animas overdrive. when his overdrives nearly full summon a weak aeon that you wont want for the battle and let the aeon take the damage from the overdrive so the party members arent damaged.