Writhing

Dark, also translated as "Writhing", 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 III

 * Writhing Shard: Shadow
 * Writhing Stone: Shadow, Fluttering
 * Writhing Gem: Fluttering, Helmed Body

Kingdom Hearts II Final Mix

 * Dark Shard: Chest at the Borough; chest at the Bamboo Grove; chest at the Village Cave; chest at the Rampart; chest at Agrabah.
 * Dark Stone: Chest at the.
 * Dark Gem: Chest at the Gorge.
 * Dark Crystal: Chest at the Corridors; chest at the Canyon.

Kingdom Hearts III
Writhing Crystals can be synthesized once 35 different synthesis materials are obtained.
 * 1 Wellspring Crystal
 * 2 Writhing Gem
 * 3 Writhing Stone
 * 5 Writhing Shard

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)

Kingdom Hearts III
Writhing materials are used to synthesize the following items:
 * Ether (2 Writhing Shard)
 * Hi-Ether (3 Writhing Stone)
 * Mega-Ether (3 Writhing Stone)
 * (2 Writhing Crystal)
 * Heartless Maul (1 Writhing Crystal, 2 Writhing Gem)
 * Heartless Maul+ (1 Writhing Crystal, 2 Writhing Gem)
 * Shadow Anklet (2 Writhing Stone, 5 Writhing Shard)
 * Dark Anklet (2 Writhing Stone, 5 Writhing Shard)
 * Midnight Anklet (2 Writhing Gem, 5 Writhing Stone)
 * Chaos Anklet (2 Writhing Gem, 5 Writhing Stone)
 * Dark Chain (3 Writhing Stone)
 * Writhing Crystal (2 Writhing Gem, 3 Writhing Stone, 5 Writhing Shard)

Writhing materials are used to forge the following Keychains:
 * Shooting Star LV5 (1 Writhing Stone)
 * Shooting Star LV6 (2 Writhing Stone)
 * Shooting Star LV8 (1 Writhing Gem)
 * Shooting Star LV9 (2 Writhing Gem)
 * Shooting Star LV10 (1 Writhing Crystal)

Notes and References
Noir Finster