In Kingdom Hearts II, Reversal is a Reaction Command that allows the user to slide behind specific enemies. When successfully executed against Dusks, it confuses any nearby Dusks and Creepers, giving the user an opportunity to attack. When used against bosses, Reversal instead allows the user to evade projectiles like the Twilight Thorn's thorn beams.
In Kingdom Hearts Birth by Sleep, Reversal is a movement command exclusive to Ventus that has a maximum level of 1. By pressing just before a targeted enemy strikes, Ventus slides behind the enemy. Equipping Reversal allows Ventus to equip the reprisal command Reversal Slash.
In Kingdom Hearts III Re Mind, Reversal is a Situation Command exclusive to Roxas and can be used when close to an enemy to slide behind them in slow motion. Attacking at the end of the slide causes Roxas to perform a powerful swinging attack similar to his Whirlwind Swing attack from Kingdom Hearts II Final Mix.
Kingdom Hearts II
Kingdom Hearts Birth by Sleep
Kingdom Hearts III Re Mind
Kingdom Hearts Birth by Sleep Final Mix