You must be seriously under-levelled then, or your strategy isn't working. Shiva should be enough to at least take Anima down to near-death.
K, if you want a REALLY hard RPG boss, Yaksa Meganada from Digital Devil Saga 2 has had me levelling up and learning skills for the past 4 hours of gameplay, and I still can't beat him.
He starts by being immune to physical attacks and using nothing but physical attacks. Then, after he's been dealt about 2000 damage, he's begin using a powerful, multi-hit move that can kill your entire party and is unblockable. At about 3000 or so, he'll change to his magic form, and get at least 4 turns every round. If he exploits a weakness, he'll get more. Oh, and he's now immune to all magic save electricity, which he absorbs.
At about 4000 damage he'll use a lightning move that WILL kill the entire party unless blocked. He'll also use status magic, meaning if a certain character is in your party you're gonna get raped.
By the way, he's got 9000 hit points. I basically need to find and learn Debilitate on the skill grid if I want to avoid getting slaughtered every time.