Writhing

Dark (うごめく) is a material type available in Kingdom Hearts II. Dark materials contain the essence of darkness, and are colored black.

Design
Dark materials are represented by black jewels with slight dark green highlights. They have an Elemental material structure.

The material's name clearly references its dark coloration and the "essence of darkness" it contains.

Kingdom Hearts II

 * Dark Shard : Shadow (4%), Soldier (8%)
 * Dark Stone : Assault Rider (12%), Nightwalker (10%)
 * Dark Gem : Gargoyle Knight (10%), Gargoyle Warrior (8%)
 * Dark Crystal: Air Pirate (8%)

Kingdom Hearts II
Dark materials are used to synthesize the following items:
 * Power Band (1 Dark Stone)
 * Buster Band (1 Dark Stone)
 * Garnet Ring (1 Dark Shard)
 * Diamond Ring (1 Dark Shard)
 * Mythril Ring (1 Dark Stone, 1 Dark Shard)
 * Orichalcum Ring (1 Dark Stone, 1 Dark Shard)
 * Soldier Earring (1 Dark Gem)
 * Fencer Earring (1 Dark Gem)
 * Expert's Ring (1 Dark Crystal, 1 Dark Gem, 1 Dark Stone, 1 Dark Shard)
 * Master's Ring (1 Dark Crystal, 1 Dark Gem, 1 Dark Stone, 1 Dark Shard)
 * Elixir (1 Dark Stone)
 * Megalixir (1 Dark Stone)
 * Drive Recovery (3 Dark Shard)
 * High Drive Recovery (3 Dark Shard)
 * AP Boost (2 Dark Crystal)
 * Magic Boost (2 Dark Crystal)

Notes and References
Noir