This was inspired by the modified dbs I slapped together for the Fatal Fury game I was entertaining thoughts of a while back. One of the main things is to make some dummy status conditions to turn the player's character invisible while his animations are running, and to keep him from attacking at the wrong times since you will be using a "fight" type command as the foundation for your event trigger.
The last time I built this system I used AP/Stamina that counted down with every command, but this time there is an invisible countdown during the player's attacking turn, and any commands after it are thrown out. I noticed, though, that if you use the in-game timer feature, when it counts down to zero the screen fades out and then comes back. To avoid that, I just set the expiration threshold higher so it never zeroes out. You end up with about four seconds max time unless you use heavy strikes or otherwise choose to end early. I'd make different animations for the same attacks, some that would be shaved to run faster. Doing attacks that would naturally flow together would use the faster animations and mean more commands allowed in the time limit. As it is, it seems that a nine hit combo is the top end for now. You can also end the turn without attacking, if you just want to focus on defending from a really nasty series that is coming up. Canceling out of an attack increases your native defense stat temporarily.
I'm planning to add in another event to check how often the player uses the same combos in a given battle. That way, if a player were to attempt using the nine hit combination every turn, the opponent would be able to predict, parry, and riposte accordingly. This would have to be tested and balanced thoroughly... although I doubt the situation would arise where the player exhausts every possible combination in a battle and ends up unable to attack without getting hammered. Although, since the player does have the option of an aggressive defense (see below) they wouldn't necessarily be up the creek.
The "Just Defend" option worked really well with this sort of setting. The enemy's attack animations are split into parts that play in sequence. If you're watching/listening you can pick up the cues for what type of attack the enemy is going to use. If you enter the correct directional input before a certain phase of the animation finishes, you'll block and take no damage. (In the other one I had where you could just hold back to do a regular block and take decreased damage, but it also inflicts a status that slows down your next turn.)
I kept screwing up when I was recording this, but if you manage to block when the enemy does one of the four hit frenzy combos, you can do your attacks on the enemy's turn, basically getting an extra turn out of it. If you combine that with the fact that enemies will all have a weakness to a different combination of attacks that 'stuns' them and allows your party (when available) to gang up on them, you could end up doing a three person ambush on a boss during the boss's attacking turn.