There are many ways to earn this, but I'll give a simple way I accomplished this.
Whenever you are on a level where you have to clear Dark Fragments make sure you have the Hex Breaker assist that let's you destroy one layer of the Dark Fragment. Use that on the last move and this will pop. The earliest is level 7 or 8.
I did this on Level 21 without too many problems. The levels before I feel are actually too easy so you'll almost always win without even needing the assists. Once you get past the early levels the game starts to actually become somewhat challenging and the assists can help you get over a level after failing.
If you played Hexic (Windows)
and already unlocked this on that version and you used all your assists there is a workaround so you can earn this without paying for more assists.
Delete the game and redownload it. Set your phone to flight mode and load the game up. Play the tutorial levels until you get the hex breaker assist then use it on the last move of the next level. Connect your phone to the internet again and let the achievement sync. I would suggest deleting the game again to avoid any potential loss of progress. The next time you launch the game when connected to the internet it should keep your progress from windows 8.