The cubes are probability-based enhancement items used to upgrade the Potential stats on your equipment. Potentials provide massive stat boosts, making the cube system one of the most vital forms of character progression in the game.
There are currently 5 types of cube, and each cube has a certain probability of the item being upgraded to a higher tier (Rare, Epic, Unique, Legendary).
You can upgrade all equipment up to 3 potential lines. Once your equipment reaches 3 lines, it is automatically displayed as a Legendary Item.