This magical creature is said to systemize and store all Dark-related knowledge that Metal Units can hold within them. A researcher has estimated that their memory capacity is no larger than that of a Metal God. However, where a Metal Unit lacks in the capability to process repetitive entities, Crystal Units are able to precisely organize such records. The density of the information they hold is said to be the reason why more experience can be gained out of them despite similarly reported capacity attributes.
Dark Crystals are best used as an ingredient for fusion, providing a base of 151,524 XP. When fused with Dark element units, it grants 227,286 XP, not including Great Success (x1.5) or Super Success (x2). The unit sells for 150,000 Zel.