There are 3 unused rune Crystals in the game's code:
Shrike crystal: Permanently attached to Kasumi and cannot be removed or obtained otherwise.
Falcon crystal: Same as the Shrike crystal but attached to Valeria.
Flame crystal: Its description reads "Bell's rune". This rune cannot be attached to any characters, and Ronnie Bell already has her own unique rune, the "Hate Rune".
Contributed by Dazz