This achievement can be earned playing in Free Mode. You must play all 45 scenarios, which is each side of each map amd finish it on Chaos difficulty. It does not matter what character you use. You do not have to finish any level Targets for this achievement.
Playing on Chaos mode in DW6 is not so much a test of skill as it is a test of patience. The quickest, best advice I can give is to use a character that is powerful against enemy generals using a weapon with FLASH on it. Also, a horse with near or max stats with Musou Spirit on it is a huge plus. I will be writing a small companion guide to go along with this achivement guide that covers, among other things, how to get through chaos mode with minimum aggrivation.