hmm very good strategy is Sarah spell
High Fly Strike, inflict Delay on Gaes.Best spell on Gaes with Sarah
Sarah
equipped with Sanctum Words - one time I take between 3000-5000 (with Critical of course) with one cast.Аt the beginning of the battle this magic is not strong to say!!!
After you downloading a bit of "Gaes skin" , he becomes more vulnerable to it
-Wendala - may use All Laxius spells, especially
Laxius Torpedo, inflict Instant Break sometimes.
My Random (used once Tunder Storm, Chaos) and Luciana don't have very good and strong spell for Ocean Gaes and they used healing items to restore HP/MP.
edit : what 10 min
Minimum to defeat Gaes is from 30 to 40 minutes
And don't forget boost Weapon Boost/Haste (not very important but still)
Gaes gave me
Esclachaboom - 16HP permanent