WARRIORS OROCHI 3 Ultimate

One of the techniques that can be done in this game is the triple rush. To enact this, hit the character switch after your active character connects with a charge attack (any attack generated from the Y button, either standalone or finishing a combo). This will cause one of your allies to jump in with a rush attack. As that happens, switch to the third character for another rush attack, and then finally back to your starting character for the third rush attack to finish up the triple rush.

In this game, there are certain 3-warrior combos that will trigger a much more cinematic and devastating rush attack. For this achievement, you need one of those.

The earliest you can get this is after Chapter 1's Battle of Yiling. This unlocks Pang De and Ma Dai. These two can be partnered up with Ma Chao for one of the required combos. Team up those three for your next battle, unleash a Triple Rush, and the Achievement is yours.

Just to add to the above solution, to trigger the special version of the attack for any given team, the character switching must be initiated in a certain order. So if it doesn't work for you simply try the triple rush in a different order. Also if you want to know the team that’s needed for the special attack for any given character just go to the "officer info" in the "preparations" menu while at the camp and press X to check additional info. There, next to the character's portrait will be a small window with the portraits of the characters they can do a special triple rush with. If one or both of the portraits are missing it means you simply haven't unlocked the character yet.