is supposed to be an unwinnable boss fight, at least during the first playthrough.
It's possible to defeat said boss during the first playthrough on the hardest difficulty setting (hard), but it requires a bit of preparation and grinding. It's not necessarily worth the effort (the boss yields a lot of EXP and a Zero Rebound Orb), but winning the boss fight slightly changes the following cutscene. Beware that I used the pay-to-shortcut DLCs that speed up grinding (EXP x 3, weapon EXP x 3) and make battles easier (damage x 2, no skill costs).
First, I recommend grinding (in Ophidian's Den) until the party has reached (around) level 40 while maxing out one of the beginning weapons for each party member (so that they can utilize all skills). While you're at it, it doesn't hurt to obtain 2 Steel Rabbit Ears (armor for Cynthia and Laminah) from Popping-Ears Bunnies (these are the enemies that sometimes hide in Happiness Barrels). Afterwards, repeatedly clear the highest feasible arena course ("silver" on "normal" or "hard") until you can afford the arena weapons and equipment (though Cynthia and Laminah can continue to wear their Steel Rabbit Ears). Then grind again (in Ophidian's Den) until you've learned all skills and can control all burst settings (at 1150 P) - my party reached level 46 during this process. Don't forget to set up your burst skills - it's recommended to turn all burst settings off except for the three strongest offensive skills (a minimum of three skills must be switched on either way). When Anemos has learned "Savage Blessing" (at 1000 P, I think), position him as the first party member (via the menu's formation command) and let him use said skill while you're grinding, since it quadruples EXP and Gold earned.
With regards to Orbs, I used Double Motion Orbs (2 actions) and Falcon Orbs (first action at the start of the battle), which can be bought from Shady Merchants or the menu's shop. It's important to act first (and often), since the boss can still one-shot everyone at this point. Even more important is that all party members' burst gauges are full at the beginning of the battle. You can simply unleash your bursts right from the start, or you can debuff the boss first (Anemos must be placed as the first party member via the menu's formation command) and then unleash your bursts. I did the latter, and it was barely enough to defeat the boss without granting him a turn, so it's obvious that you'll have a much harder time without using the damage x 2 DLC. If the boss survives the initial onslaught, don't waste your time with healing, but revive all knocked-out party members as soon as possible (preferably by using Anemos' "Backup Plan" skill, since it also lets the revived party member act immediately afterwards) and stay on the offensive. And don't forget: You won't miss anything of importance, and you can still beat this boss on subsequent playthroughs (as intended by the developers), so only attempt this challenge if and while it's fun (and better fork over your money for the DLCs).