Shield (シールド, Shīrudo?) is a spell that grants the Shield status to one ally, making them immune to physical and elemental damage. However, they can be still damaged by non-elemental magic or items. It costs 180 MP and comes on the magic materia Shield, but one must level it up by getting 10,000 AP for it before it can be used.
Take less damage, but Overdrive gauge won't charge.
Shield is a command which allows aeons to shield themselves from damage at the cost of not charging the Overdrive gauge. It is especially useful for when the player knows when a particularly strong attack is about to be used.
While the aeon may not typically take much damage from the basic attacks of an enemy, some enemies such as Greater Sphere can use abilities that deal a fixed percentage of a character or aeon's maximum life. Shield can reduce the damage of even these attacks to just a quarter of the normal damage and even be paired with Protect or Shell to reduce this percentage to an eighth of the typical amount, making otherwise tough battles much more manageable for an aeon. Shield is useless against the Cactuar's 10,000 Needles and the Cactuar King's 99,999 Needles as the damage is still the same, however the Qactuar's 1,000 Needles can be reduced to 250 by Shield.
Shield is the unique ability of the Floral Fallal special dressphere, learned for 20 AP and costing 36 MP to cast, and can only be learned after learning the ability Barrier. It completely nullifies all physical damage done to Yuna herself, but not to the Pistils.