Data Crystal (データクリスタル) are item drops that are produced from the slain bodies of monsters in YGGDRASIL.
One of the fundamental building blocks in YGGDRASIL, these crystals are what make the flexible system of customization in YGGDRASIL possible. Data crystals can be used in customization for all facets of the game, ranging from changing the qualities of locations, crafting NPCs, designing personal weapons, altering player appearances, etc. However, harvesting data crystals is difficult as they do not usually come with the same quality as they always do.
It's a small crystal that was used for the storage of data, very similar to a data card or memory crystal.
The possible uses of data crystals could be considered endless such as upgrading a player's standard gear to Divine Class. In order to craft a Divine Class item, certain materials are necessarily needed to make one. YGGDRASIL magic items are created from these embedded computer data crystals. However, since the performance of computer data crystals dropped by monsters is uneven, the manufacture of Divine class items makes it necessary to have several “extremely rare loot” computer data crystals for it to be possible. Simply put, if a player wanted these computer data crystals to be embedded into a container such as a sword-type weapon, it had to be a weapon forged from ultra rare metal for it to be possible.
Though data crystals allow for near unlimited customization, there are actually limits to their abilities. For example, data crystals are unable to produce items that did not originate from the game like Clementine’s stilettos.