Boss: Holly Whyte
Meanwhile, the nurses use This Might Sting to attack one and potentially inflict Dread and Cure to heal low HP. After you defeat the nurses, Holly will eventually summon more with Reinforcements, but they're easily taken of.
Since all of the girls have terrible physical defence and Holly has incredible magic defence, physical attacks will be your key to victory. The nurses don't like being struck with lightning either. As long as you keep on the offensive, this battle is a breeze.
Boss: Erutus Profiteur
The Merchant's other trick is Pay to Win, which boosts his or his allies's critical rate. Fortunately, this won't affect Takeover's damage, but if he has lackeys around, their physical hits will hurt more.
Speaking of lackeys, the Thug likes to use Eye Gouge to inflict blind on one. Other times, he will Brave and use Psych Up to boost his attack before letting loose a Strong Strike. Meanwhile, the Mage casts Fira to set a character alight and Sleep to send one to sleep.
Finally, the Blade is keen to use Carotid Slash to drop a character's Magic Defence. Focus on the Thug so your physical attackers can fight safely, then move onto the Mage and Blade.
Once you've singled out Profiteur, the battle should become manageable. If your characters are around Level 23, they should have over 800 HP, so simply keep healing anyone who takes damage. If their HP is less, you can use Damage Dispersion (Wizard ability) to spread out the damage.
For offence, most attacks should be fine as Profiteur has balanced defences. The best time to attack is the turn after Profiteur Defaults, when he Braves for two Takeovers. Since Defaulting doesn't reduce Takeover's damage, you may as well attack while he's not Defaulting.
Compared to previous bosses, Profiteur has a lot of HP and can take a while to take down. If you have Special Moves, use them. The Astrologian's Physical/Mystic Boon combined with the Mist Spellcraft will be useful to boost your firepower as well.
If you start running out of MP, don't be stingy and use your Ethers--they're expensive for sure, but you'll earn the money back with More Money... if you win the battle that is!