The fight against Luca Blight is a difficult battle. He can easily level your entire party if you don't come prepared. With this glitch, it will be impossible for him to defeat you. Here's a rundown on what to do.
1: Before heading into the war room and moving out, make a party of 6.
2: With the party of six, make sure you put Riou in the 4th (bottom-left) slot.
3: Head into the war room.
4: When assembling your parties, Riou will appear to be in the first slot.
5: DO NOT put anyone else in Riou's party.
6: Go fight Luca.
7: When you're at Riou's part, Luca will not attack at all. Pick at him with Riou for the easy win.
For the first two fights, you don't have to win them. If Luca beats your first party, he will move on to the second. When he beats the second, he'll move on to the third. The third fight is the battle you have to win. But, with this glitch, it'll be impossible for Luca to win that third battle, gaining you an easy win over the toughest battle in the game.
You must have already recruited the armor shop owner to your armies cause for this trick to work. Once this has been done, go to his shop. This glitch involves some simple calculations, use the following example as a guide to see how it is done. Equip one character with Dragon Armor (23,000 potch), and make sure that at least two other characters have no armor equipped, but can wear Dragon Armor. You should also have 23,000 to 30,000 potch. Talk to the armorer, go to buy, then choose to purchase Dragon Armor. When prompted to place it in the bag or to equip it, choose to equip it on the character already wearing Dragon Armor. When prompted to sell the old armor or put it in the bag, cancel the action. You should still be in buying mode for the armor. Simply purchase and equip the two armorless characters Dragon Armor. The potch meter will reset to somewhere around 999,999.
To take part in this in-game cheat, you must have at least one of the Stones (i.e. Stone of Power, Stone of Defense, etc.). Having multiple stones speeds up the process of gaining stats.
NOTE: Make sure to SAVE your game FIRST before you try this!
Use the stones on any character, then enter a battle and lose. (Tip: Unequipping all armor before the battle makes it faster to lose.) At the game over screen, don't give up. It will reload you to your last save. You will retain all of the items you previously had before your character died (i.e. the stones). You will also retain the stats that you gained from the stones.
This can be repeated any number of times on any character.
Each character can wear different types of armor, and some can not wear some types of armor. However, there is a trick to get around this. Just exchange equipment directly from the individual character's inventory! It is easy! However, the person who is giving the unequipable armor to another has to be able to equip the armor that the other person is wearing. For example, if Humphrey is wearing Knight Armor, and Luc has a tunic on, you could do this because Humphrey could wear tunics, however, if Luc is wearing Magic Robes, this will not work. Also, if a character is wearing non-removable armor/accessories this won't work, and characters that can not use shields can not have shields swapped.