KINGDOM HEARTS HD 2.8 Final Chapter Prologue

In the World That Never Was Sora and Riku will come across objects you need to use reality shift (activated by pressing B+Y together) on to advance. This will put you into a pretty straightforward minigame where you have to cut different coloured chains. Simply wait until all the parts you need to cut are lined up in a row and press A to go through them all in one go. Repeating this 3 times in a row successfully should give you the achievement, though I personally found I had to do it a few more times before the achievement actually popped for me.

You can also activate this minigame in battle by hitting enemies until the lock on symbol turns purple and then using Reality Shift on them. How frequently this occurs will depend on what Keyblade you currently have equipped.