From the Kingdom Hearts Wiki: A world of information not accessible by Gummiship
Dual Smasher (クロススマッシャー, Kurosu Sumasshā?, lit. "Cross Smasher") is an ability in Kingdom Hearts III. It allows the user to counterattack after a successful block by charging at the enemy with crossed Keyblades.
In Kingdom Hearts III, Dual Smasher is an action ability. It is activated by pressing after a successful block using Dual Guard.
Learning Dual Smasher
Kingdom Hearts III