If you're struggling on beating the boss here is the way:
Try doing mystery dungeon to make awesome amounts of money, probably you wont be able to go to end of it at start but it’s ok. Then invest all your money on blacksmithing books. If you didnt get “Redemption” recipe by now load game a few times until you see it at the shop. When you reach a decent lvl at blacksmithing you will be able to craft the weapon. It’s the best weapon I’ve seen for sword users.(If you’re archer or mage skip this step, or craft 1 high end bow/staff/books)
Second step is lvling your alchemy. Alchemy has a recipe named oil of enhancement. Do shopping trick to find the recipe if you dont have it. This time I suggest you to max your alchemy because it’ll only reach up 50% chance. That oil increases your weapon dmg. If you make that recipe around 10 times, you should be able to 1 shot pretty much everything in game.
 "Arkandian Crusade")