WARRIORS OROCHI 3 Ultimate

This achievement will be unlocked during normal story progression. This is the last stage of Chapter 6, and is unmissable if you're playing through the story normally. You may notice during the stage that many of your team-mates lives are in critical danger, but don't worry about it, it's just due to the poison mist. As long as you don't let them get beat up by the enemy officers, they'll just run past all the soldiers and not take any damage, and plus the poison mist won't kill them outright, just lower their health to the critical state.

Just a little addition to make here: if you, like me, didn't get the cheevo to pop the first time around, for whatever reason, exit the game completely and start it back up. Replay the stage without turning off the system or allowing it to sleep. For reference, I played it on hard using a maxed out Zhang Liao. It popped during the battle results screens. This seems to work for all of the stage completion achievements so far, as I didn't get any of them the first time around.