Huge Hit: Swipe in one direction, then the opposite then the opposite of that, i.e., left, right, left, right for the last strike to deal 200% damage.
Mega Hit: Swipe twice in one direction, then twice in the opposite direction, i.e, left, left, right, right and the last strike will do 250% damage.
Ultra Hit: Swipe once in any direction, then in the opposite, then once in a way you haven't already, then the opposite, then the opposite again, i.e., left, right, up, down, up for a whopping 300% damage
I've noticed that one type of hit is more appropriate for one type of opponent off-balance state. The Ultra-Hit is most successful with a perfect parry, as the damage multiplier is increased as well as the opponent remains stunned long enough to deliver all five blows.
These strategies are applicable to online duels as well.