The Chosen Ones

Richie: There are a plenty items that gives  smth like 10% to 30% of steal chance, if you get the best ones and equip them you'll probably steal it without(or maybe with a little) problem.
Oh, and if you don't want to equip the "steal" items because they're far too weak, i have bad news for you. Another thing you can do is increase the agility of your Fradz, that too increases the steal chance.
Of course there's always a chance that the "steal defense" of the boss is unbalanced.