This magical creature is said to systemize and store all Earth-related knowledge that Metal Units can hold within them. They seem to be able to communicate with Earth Ghosts, who are known for their reticence, solely by gaze. Due to that, they attempt to communicate by gaze with others as well, only ever saying "It's fine, it's fine. You don't have to say a thing." It has been said that gazing into one's eyes instills a sense of recognition and positivity. However, there are a few rare rumors saying that they don't really think of anything and have no intention of listening to anyone.
Earth Crystals are best used as an ingredient for fusion, providing a base of 151,524 XP. When fused with Earth element units, it grants 227,286 XP, not including Great Success (x1.5) or Super Success (x2). The unit sells for 150,000 Zel.