This requires you to score "GOOD" or better ("Great", "Super", "Perfect") on every move in a single song. That is, you cannot get "Ok" or an "X" for any of the moves. If you do, either restart the song, or try again later.
This will probably come naturally as you play the game working towards other achievements.
It's maybe worth noting you can do this on a JD Unlimited song, it doesn't have to be a JD 2021 song. So if you're struggling or anxious to get this out of the way, play Baby Shark from JD 2020 a few times and you'll have this in no time (that song is very easy, and very short, though also very annoying to listen to).