The kasha was a crystal traditionally used by the Cereans as a meditation tool. They were used to clear the mind of distractions in order to create a perfect meditation environment. Patterns were scribed on each face of the crystal to harness its full energy potential, possibly created by Bi-Dar Tyunda thousands of years before.
When used as a lightsaber crystal, it helped clear the wielder's mind of distractions, even during tense combat.