To customize a weapon with Distill Mana, you’ll need a weapon with a blank ability slot and 2 Mana Spheres. The weapon’s name may change after adding the ability to it.
Where To Get Mana Spheres
You’ll find yourself with a steady supply of Mana Spheres near the start of the game. But this may change as soon as you start customizing equipment and Aeon abilities. However, there are plenty of fiends across Spira that drop Mana Spheres. Here’s a list of fiends that drop Mana Spheres without needing to use items or abilities: Enemies outside of the ones listed above may drop Mana Spheres through the use of Mana Distillers or abilities like Bribe and Extract Mana.
Using Distill Mana
All you need to do to use the Distill Mana ability is equip the weapon that has it and hit an enemy with a basic attack or skill. Once you do this, that enemy will be tagged with the Distill Mana status. Being hit with the Distill Mana auto-ability will have the same effect as using Mana Distillers and the Extract Mana skill. The effects from these sources will not stack with each other.