It helps to have Tetrakarn, or a physical mirror. Have plenty of buffs on hand like Rakukaja, Tarukaja, Sukukaja,Tarunda etc.(this is important) If you have a demon with Bomdi, that will help because the entire battle can be over if you get screwed by one of your demons exploding. I would dedicate Nemissa, or another demon to healing every round.
I remember it took me a while to beat this fight as well. Try raising levels if you're still having trouble, but basically set up physical reflect, then debuff and buff right away.