Skill crystal

Skill crystals (aka monster cards in the web novel) is a rare drop from demons.

Appearance
Skill Crystals are about the same size as Intelligence Cards. They also appear to be blank.

Description
Skill crystals are demon drops that, when fused to a piece of equipment, will bestow upon that equipment a skill that depends on what kind of skill crystal is used. Only a Master Smith can perform skill crystal Fusion. skill crystals can only be identified using a Guild Temple.

Trivia

 * They are known in the web novel as monster cards.
 * Skill crystals are very rare drops, as it seems that there aren't a lot of them in circulation; the only other way to get them is through auctions.
 * There are skill crystals that are called high-ranked skill crystals that can only be used when fused to an equipment together with a High Kobold skill crystal.
 * Most people believe that skill crystal fusion relies on luck. This is false as a skill crystal Fusion will always succeed as long as the item has an empty skill slot. If there are no more empty skill slots, then the fusion will fail, the skill crystal will disappear, and the item will be reduced to its raw materials.
 * Michio uses Appraisal to tell if an item has an empty skill slot or not.