The easiest Brutality to preform, by far, is Raiden's. His first Brutality is called Super Shocker, and can be accessed from any of the three variations. There are no health stipulations or special requirements. All you must do is win the fight with his "Electrocute" special attack (
) as the final attack, and be sure to hit
3 times during the animation. It can be on any level, against any opponent.
Edit: As mentioned by kelle1994, Takeda's brutality only requires you to grab your opponent with the final hit of the match, and hit X four times during the animation.