Attack preemptively before being attacked.
First Strike is an ability learned by the Monk class for 1300 JP (1200 JP on the PS). While equipped, the user will always attack first before an enemy attacks them if it is a physical attack and they are in range of hitting the enemy.
Block enemy attack and counterattack. Ineffective vs. A-abil.
Strike Back is a support ability learned by the Parivir, Gladiator, and Ravager for 250 AP from the Bone Plate. The ability allows the user to block an attack (not skill attack) and counter it with their own physical attack.