The Rush is unique to Suikoden IV, after several battles the rush meter (the yellow bar at the bottom of the fight screen) fills up and the rush option becomes selectable. Doing so all the party members give energy to Lazlo healing him, and then Lazlo steps forward swings his blades outward, sending out a wave of energy that does severe damage to all enemies.
It should be noted that since you did not have to choose the attack option first that this does not count as a attack round. Meaning that your enemies can not attack you that turn. However once you use it your Rush meter is depleted and returns to zero. Also the Rush meter remains in its place even after the battle.
Lazlo En Kuldes
Any three conscious party members (no one can be asleep).