Demon equipment

Demon Armor, also known as Demon Mail or Demon Vest, is a recurring armor in the series. It is associated with the Dark element, usually allowing the user to absorb or reduce damage done from Dark elemental attacks. Its rank usually varies depending on the game it appears in, though oftentimes it offers high defenses.

Final Fantasy III
Demon Mail is a high-ranked armor that can be used by heavy melee classes such as Knight and Dragoon. It offers +38 Defense and +17 Magic Defense.

Final Fantasy IV
Demon Armor is the last armor that Dark Knight Cecil can equip, and is thus the strongest Dark Knight armor in the game, even though it is early in the game. It provides +9 Defense, +3 Magic Defense, -10 Evasion, and can be bought for 3000 Gil at Fabul.

Final Fantasy IX
Demon's Mail is a mid-rank armor that can only be used by Steiner and Freya. It provides +27 Defense, absorbs Shadow elemental attacks, and increases the damage of the user's Shadow elemental attacks. It teaches the ability High Tide. The Demon's Vest can be used by everyone else except the above two, and provides +31 Defense, +1 Magic, and halves Shadow elemental damage. It teaches the abilities Auto-Potion, Devil Killer, and Locomotion.

Final Fantasy XII
Demon Mail is a mid-rank armor that requires 40 LP to use and can be bought for 4900 Gil. It provides +29 Defense, +5 Strength, and +3 Vitality.