I couldn't finish 'em. Looks like this's gonna get complicated.
This mad bearer of the salve-maker's asterisk uses Dark Breath, a terrifying attack born of his compounding skills. The less HP he has, more damage it will deal.
Qada will open with Water of Life, which applies a Regen effect on himself, healing 1200 HP each turn. His Poison Hi-Potion attack will deal 1000 damage to the receiving party member, and is capable of inflicting the Poison status effect. Dark Breath will do damage equal to Qada's lost HP, and thus will likely KO its target when used. Dark Breath can be devastating to the whole party or even kill everyone if the victim uses Black Mage's Damage Dispersion, causing the potential 9999 damage to be dispersed as follow: 6499 damage dealt to the victim (or more if a party member is killed), and 1500 to each of the other alive party member, potentially killing them in the first world. It is strongly recommended to disable this ability before the fight.
First World Edit
One should go into this battle prepared to do tons of healing, so a Red or White Mage and an additional character with White Magic equipped is a necessity (having plenty of restorative items is recommended too). It's also wise to have everyone equipped with a Star Pendant (bought in Ancheim) or the Freelancer's Poison Immunity support skill (learned at job level 9). Qada will often use Water of Life to grant himself Regen status for ten turns, so use the White Magic Dispel spell to cancel it out, otherwise he can restore all the damage dealt to him at the end of the turn. Be prepared to revive characters, because his Dark Breath technique is all but guaranteed to KO them. He usually defaults for one turn before using this attack, so be prepared for it when he does. His Poison Hi-Potion is also guaranteed to deal 1,000 damage, so it can be devastating if ones HP drops too low, especially if he couples it with his Dark Breath attack in the same turn.
When not healing the party, use those turns to attack him with physical or offensive magic attacks.
Alternatively (especially in the repeated battles), one can forego the anti-poison equips and instead use the Red Mage ability BP Recovery, which grants a target two BP every time they're infected with a status-ailment. With two extra BP at one's disposal, it's a simple matter to remove the poison status and then use the remaining two BP to either heal or attack, or both (it's easier to do this in the repeated battles due to higher HP and his attacks—excluding Dark Breath—aren't quite as devastating).
His strategy does not change in subsequent battles in the second and third world, though his HP and stats are raised significantly.
Fourth World Edit
In this battle, Qada is fought alongside his colleagues DeRosa and Chairman Profiteur. Since Qada is no longer the only enemy for the party to fight, it is advised the player leave Qada for last in this battle so that his main form of damage and KO capability, Dark Breath, is essentially harmless for the duration of the battle while the player focuses on the other two who are more capable of dealing damage. He still possesses the ability to transmute Poison Hi-Potion and Water of Life, however, so the player must deal with these effects accordingly during the course of battle.
Fifth World - Stark Fort Edit
In this battle, Qada fights alongside with the Black Blades; Kamiizumi, Barbarossa, Praline and Kikyo. His strategy does not change from the fourth world and the player may repeat the tactic of leaving him last due to Dark Breath.
Fifth World - Central Command Edit
Grouped with Ominas, Mephilia and Sage Yulyana, this group is considered to be the toughest of all the others in Central Command. Qada now possesses the ability to transmute Fire Bane, which debuffs the party with weakness to fire-elemental damage, and also removes Fire Immunity and/or Abate Fire foiling the player's attempts to negate fire damage. Coupled with Ominas now using Firaga and Mephilia opting to use Promethean Fire, the party will suffer devastating damage and may be wiped out when the two spellcasters act after Qada's setup.