Before going into the Story mode, head into the Options menu and put the the game on Cake Walk difficulty. Not needed, but if you want this achievement more easily I would recommend doing this. The best character I found to do this with is Dive. He jumps very high and his kicks are easy to land. Pick him, and pick the YOLO gem. What is the YOLO gem you might ask? Well, basically, you have to win all 5 rounds without losing once. If you lose a round, you lose the match. The hardest person to beat is S-Kill, the last enemy. The way I killed him was that I constantly spam the dive and kick button. Once you beat him, it will unlock.