Counterattack

Counterattack is an ability in Kingdom Hearts. It is meant to be equipped in conjunction with Guard. It allows the user to quickly get in an attack directly after blocking an attack with Guard, it allows you to branch the first attack off into a combo, as well. It's useful for fights where the enemy has a fast recovery rate and will generally launch right back into an attack after Sora blocks it. It can also be used when parrying an attack by perfectly timing an attack and blocking the opponents attack with it.

Note: It seems some enemies, especially later on in the game, can also use a form of this. Riku uses on an odd form in the Destiny Islands where if hit onto the ground, he kicks back through Sora. He also uses this when you fight him for the second time at Hollow Bastion. (He taunts you and holds his blade in a Guard like stance and if Sora hits it, he quickly spins around and hits Sora, often launching into a another combo right afterward)

In Kingdom Hearts II and Kingdom Hearts II: Final Mix+ it is referred to as Counterguard

Description
Use with Guard to recover MP with a successful Counterattack