Elemental Materia/Final Fantasy VII

The Elemental Materia allows the equipped player to imbue either a weapon or armor with elemental properties from a corresponding elementally-aspected materia. If linked in a weapon, the weapon deals greater damage against enemies weak against that element, but can also cause less damage against enemies strong against that element; in some cases, an enemy might even be healed by such a combination. If linked in armor, it can reduce damage taken from a certain element.