Monk's are the best magic users. If you want to take 9999 damage with fire. Not fira or firaga, but fire. Equip the monk's natural talent and spell fencer's phantom weapon. That'll leave them with low defense though so using commerce's low leverage will reduce all damage by half. Since the monk hits the damage limit with just fire, you'll probably hit the damage limit with fira or firaga while low leverage is activated.
White mage can be the one equipped with commerce, but also the skill with holy one if needed to cure. The one class I mentioned above to max out BP every turn. Two monks should decimate even the last boss no problem.







