The most annoying factor of this battle, and what makes it last so long, is that every turn the monster gains back 88-91 HP, so unless you do more damage than that in one round of turns, you probably lost ground. Your going to want Alex to use Vigor to power himself up and then his Sword Dance. Luna should cast Cascade on Alex to make him even stronger, and then heal the other members of the group. Nash should use his Thunder Bomb attack while Ramus uses his normal attack and heals with items. When Alex runs out of MP just have him use his normal attack. Hang in there, this is your first real boss, and once you get use to it, it is not so bad.