No I dont think its possible to kill seymore before he calls anima. To beat anima use aeons or use lots of phenix downs. I didnt summon an aeon until anima's overdrive filled up, then I used guard after the overdrive I dissmised the aeon. Every time anima killed one of my guys I would use a phenix down.When anima was almost dead I summoned an aeon then when it died, and seymore started casting multi magic it would just hit my aeon. Then I hit seymore with every thing I had.