Bane’s Heart was a unique carmine lightsaber crystal given to Darth Zannah by her Sith Master, Darth Bane, following the Seventh Battle of Ruusan. She used it in her double-bladed lightsaber, which she named after the crystal itself.
The lightsaber and crystal later came into the possession of a Dark Jedi murdered by Qymaen jai Sheelal, otherwise known as General Grievous, Supreme Commander of the Droid Armies of the Confederacy of Independent Systems, either on Dica or Necropolis. Grievous stored the weapon aboard his personal starfighter, which was later recovered by Imperial forces and used as part of the N-K Project. The Bane’s Heart lightsaber was wielded by N-K Necrosis during the Galactic Civil War until he was killed by a group of spacers who took the crystal from his dead body.
When tuned to be used in a lightsaber, it caused that lightsaber to release an electrical discharge and made it difficult for anyone other than the rightful owner to use the lightsaber.