Item description:

You start in Bevelle near the entrance, to Via Infinito. Examine the blue insignia, on the floor choose, Countinue from the deepest cloister reached, you'll see Paragon in the background, with small Tonberry in front of it. Your party should be 3 thieves, each with 2x Iron Duke equipped.
On this particular save file, you have 99x of every item and accessory. Anyway, examine Tonberry to start the fight, against Paragon.