Having once been in SOLDIER from Midgar’s Shinra, Zack has received prolonged exposure to Mako. Along with this energy source, he has also been injected with Jenova’s cells, an Ancient that had come to Gaia a long, long time ago. With this dual augmentation, those in SOLDIER have a far greater strength and cognitive ability than the ordinary person.
Zack once wielded the Buster Sword, but after certain unfortunate events, it was passed onto Cloud. So now, he merely uses his old go-to, the common SOLDIER sword.
He also has a few limit breaks that he can use. These are built upon the relationships he has made with the important people in his life [I’m not including all of them]:
Chain Slash: Zack’s own basic limit. Five quick, consecutive slashes are made against the target.
Octoslash: Because of the relation he had with, and the memories he has of, Sephiroth, Zack can perform the one-winged angel’s famous move. A series of eight powerful strokes.
Assault Rush: Foregoing his sword for the use of his fists, Zack strikes the enemy seven times, in two different sequences, before diving at them as a last attack. This limit is forged by the bond and memories he has of his best friend, Angeal.
Healing Wave: Can fully heal himself and remove most status ailments. The limit comes from Aerith, of whom he cherishes.
Meteor Shots: Zack leaps up, and from a swing of his sword a small barrage of meteors is summoned to assault the enemy. Because of his relationship with Cloud, Zack is able to perform this limit.