There's a symbol that pops up that indicates the next attack is unbreakable, but you have to watch and determine if it's a sweep, thrust or grab. For sweeps you have to jump, for thrusts you have to deflect and for grabs you have to Dodge.
Sounds like Brad was right then. This sounds like a single player fighting game.
This may not be here or there, and it may sound like I'm telling you shit you already know. I'll be using fighting game logic. While I haven't played the game yet:
It's not about reactions. Each enemy type should probably have their own mix. Therefore, when you meet new enemies, you should be doing data mining. Find what their move set is before committing. You cannot punish or react to something if you don't know what your options are. I'm pretty sure not all enemies have sweeps, grabs, or thrusts. It might be either/or and few enemies will have all three. So you need to probe data from enemies and do reconnaissance in battle to see what their moveset is. Since you don't know if it'll be a sweep, thrust, or whatever you need to find what your opponents options are. Once you do, you'll be able to react. Information first, reaction second. You cannot react to what you don't know. I'd do some in-out, in-out to test the enemies ranges and moveset before committing to an action.
Again, sorry if this is obvious to you and it sounds like I'm talking down to you.