Secret Gem

Secret Gem is a material available in Kingdom Hearts Birth by Sleep, and Kingdom Hearts Birth by Sleep Final Mix. It can be used during Command Meld to attach a random ability to the synthesized command, and immediately raise it to its maximum level.

Design
Secret Gem is represented by four jewels with a unique structure. The main jewel is the largest, is tube-shaped, and has facet cuts. Two medium-sized jewels are hook-shaped and revolve around the main jewel. The smallest jewel floats between the two hook-shaped ones. All four jewels are golden yellow with green tints at the edges, and the largest one has a swirling, purple and yellow, smoky design in its center.

An ore is a type of rock that contains important minerals, such as metals. "Secret" may reference the fact that the material can only be obtained through rare drops from the Flood, defeating Vanitas Remnant, or excelling in certain mini-games.

Kingdom Hearts Birth by Sleep

 * Secret Gem: Flood (1%), Vanitas Remnant (100%)

Kingdom Hearts Birth by Sleep

 * Secret Gem: Collect 100 points in Terra's Sticker Album; collect 100 points in Aqua's Sticker Album.

Kingdom Hearts Birth by Sleep Final Mix

 * Secret Gem: Chest at the Realm of Darkness: Upper Layer.

Kingdom Hearts Birth by Sleep

 * Secret Gem: Purchase from Medal Shop for 1500 medals.

Kingdom Hearts Birth by Sleep
Secret Gem materials are used to add the following abilities:
 * Fire Boost
 * Fire Screen
 * Blizzard Boost
 * Blizzard Screen
 * Thunder Boost
 * Thunder Screen
 * Cure Boost
 * Dark Screen
 * Magic Haste
 * Attack Haste
 * Reload Boost
 * Leaf Bracer
 * Second Chance
 * Finish Boost
 * Combo F Boost
 * Combo Plus
 * Air Combo Plus
 * Once More
 * HP Boost
 * Item Boost
 * Damage Syphon
 * Defender
 * HP Prize Plus
 * Treasure Magnet
 * Link Prize Plus
 * EXP Chance
 * Lucky Strike
 * EXP Walker

Notes and references
Gemme secrète Geheimes Erz