[Zifnab]

Of course. I beat the game using Anima and the Magus Sisters but it's easy without them.
Get Valefor's 2nd Overdrive, which can be found in Besaid (does around 50,000 as I recall). Get a few people's ultimate weapons to get the other aeons to go beyond 9999 damage. The last boss (well, the main one) has 50,000 HP followd by (I think) 120,000 HP, so I'd say beat the first one with attacks and your 9999 incuring Aeons, then use your better Aeons (Valefor and the rest) on the last version of it.
Anima is alittle overkill really, as she can easily knock down the last boss in one hit