The Vorban is a tough opponent because of its high HP, high Defense, and its immunity to Armor Break. It can randomly counterattack with Mortar, which hits the party for moderate damage and can use Body Splash to attack the entire party.
Vorban drops weapons with Strength +% abilities and armor with Defense +% abilities, Strength +20% and Defense +20% being fixed abilities.
To start the battle, it is a good idea to cast Shell on the party to lower the damage from Mortar. For offense, magic works well to take it down. Overdrives can be helpful as well. If the player has Anima or the Magus Sisters, this fight becomes much easier. Also, the Celestial Weapons ignore targets' Defense, and will quickly decimate Vorban.