A counter breaker is when, in the middle of a combo, you think the opponent will combo break you so this is a reaction to this.
I was easily able to obtain this against the computer in less than 5 minutes.
The combo for this is MP+MK or just back on the right thumb stick
Pick Jago and play the computer on "Easy" difficulty.
You don't need a complicated combo, in fact a simple jump kick (I was using RT) works. Jump into the computer and kick them, and then press back on the right thumbstick. If you time it right (Jago doesn't continue his combo), you will either counter break the opponent or be frozen for half a second while no one does anything. The animation for his counter break is he sticks his sword out vertically in front of him. If it does connect there is a big yellow flash and you hear counter breaker.
I found my opponent (Sabrewulf) would get me a counter breaker almost 75% of the time.