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1) Easy Way: Beat the career on Hard (including the battle with Lou) with a guitar, let it save and turn off your console. Now turn on you xbox, and start the game with a controller, select career from the main menu and the profile that you had beat hard using the guitar, and the achievement will now unlock, without ever playing using the controller.
2) Legitimate Way: To do this legitimately, you will need to use the controller. Hard difficulty won't start off too bad, but Tier 7 and 8 will be huge pain (literally) as some songs have fast strum sections that are nearly impossible using the controller. I wish you lots of luck, practice, and all the patience in the world. You can always use the guitar method (in way #1) if you are struggling with a song and are decent at guitar to help you move on to the next song. The method above will work if you mix your completed songs with guitar + controller as well.
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