Blue Soul Crystal - Stage 16หินสะกดวิญญาณสีฟ้า - 16

Blue crystal containing the light of absorbed souls. stage 16. Special abilities can be applied to the weapon when absorbing certain amount of souls. Every time it is used, it consumes 26 of MP. A crystal of this level is said to absorb crystals on its own, so it doesn't seem like you need to use it directly on the monsters.