Quick Strike is one of only a handful of stand-alone Psynergies that can be used by the player. It does not succeed any Psynergy, nor does it have a successor; it simply exists by itself.
Quick Strike is available to any of the classes in the Samurai Class series at Level 40. It is aligned with the Jupiter element, costs 12 PP to perform, and hits a single target. It works in a manner similar to the Annihilation technique; rather than having a base power, it multiplies the caster's Attack stat by 1.8. This means that an Adept with an attack of 100 will do 180 damage, and an Adept with an attack of 200 will do 360 damage. Quick Strike appears as a sudden attack, followed by the screen darkening and a large blue strike appearing on the screen.
Quick Strike is one of the more powerful single target attacks in the game. It benefits from the low Psynergy cost, and the fact that the strength is multiplied instead of just having an additional attack bonus added to it. In the original Golden Sun it is one of the most powerful Psynergy in the game, and while in Golden Sun: The Lost Age it can be outclassed by both Call Demon and Call Dullahan, as well as the 99% unleash rate setup for the Sol Blade, an Adept being a Ronin without any of those luxuries will find this extremely useful nonetheless.
To make the damage output of Quick Strike as high as possible, the Darksword, with its highest-of-the-high base attack increase, is perhaps the best weapon to equip, in conjunction with attack-increasing equipment that further boost it's base attack. The use of only the Darksword, or even the Excalibur will be needed at the near-end levels, however because the attack (999) will be maxed out, prioritizing HP, defense or resistance.