In Dead or Alive 6 every character has its own unique Fatal Rush attack which is essentially a series of four attacks that throw the opponent into a Fatal Stun if they connect. The first blow in the series of four strikes will always be a high attack while the last one will be a blow that stuns and knocks the opponent back. It is important that you choose the right moment to perform a Fatal Rush atttack as either missing the first blow or having it blocked will render your fighter vulnerable to a counter attack.
Fatal Rush attacks are performed by pressing R1 (RB) four times, once for each attack in the chain. The move itself doesn't require or consume Break Gauge but will typically providing you have meter end with a Break Blow. The only way a Fatal Rush attack chain can be broken is by using a Break Block move, this is another addition related to the Break System that does require and consume Break Gauge.
Check out the video below to see a showcase of all 24 characters and their Fatal Rush attacks.