How Do You Do A Critical Finish on Soul Calibur 4?

First you have to make your opponent block your attacks. You'll see the small diamond on the side of their health bar change color (the soul gauge), when it is red, keep slashing and eventually you'll perform a soul crush, red sparks will be visible, at that moment you have to push A+B+K+G simultaneously. The Critical Finish will be performed and you will win the battle (not the match).