For this achievement you must clear Arcade mode on Medium difficulty or higher. Arcade Mode is pretty short in this game containing seven fights of tag-team action(excluding the Boss Fight). Here's the breakdown of Arcade:
This is easily obtainable with the right team or with basic experience in the game. You can also set Rounds to 1 and use Zangief to dominate your way through the game with his abusable moves! Just make sure the difficulty is set to Medium or higher in the pre-game lobby upon selecting Arcade.
See The Root of Chaos for more info on getting through Arcade Mode easily. Regardless, this will unlock while working towards the other Arcade-related achievements.