Upon reaching a certain point in the main story, you will unlock the ability to customize your equipment. At that time, your options will be limited, but as you gain more items, you will see that there’s a plethora of abilities you can add. All equipment in the game can have one to four slots, in which to add abilities to them. All of the abilities you can add will require a specific number of a certain item in order to add it. You can add abilities to any piece of equipment, as long as it has an open slot. Once you add an ability, it cannot be removed, so you need to be careful you don’t accidentally use hard-to-come-by items. You also cannot add abilities to Tidus’ Brotherhood, nor Celestial Weapons.